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 Harare, Zimbabwe (CNN) Robert Mugabe resigned as Zimbabwe's President on Tuesday after 37 years of autocratic rule, finally succumbing to the pressure of a military takeover and the humiliation of impeachment. 
 
 The announcement came minutes into a joint session of the Zimbabwean Parliament in Harare, convened to prise the 93-year-old from power. 
 
 As the speaker read out a letter from Mugabe, lawmakers broke out in thunderous applause. The impeachment proceedings were immediately suspended. 
 
 Mugabe's successor, according to a spokesman for the ZANU-PF party, will be former Vice President Emmerson Mnangagwa, whose firing by Mugabe precipitated the crisis. 
 
 In the streets outside, crowds erupted in rapturous celebrations, dancing and cheering in joy, raising their fists and waving Zimbabwean flags. 
 
 Zimbabwe's members of Parliament celebrate after Mugabe's resignation. 
 
 It was the culmination of an extraordinary week in the history of Zimbabwe that began when the country's military leaders staged an unprecedented intervention to prevent the ascent to power of Mugabe's 52-year-old wife, Grace. 
 
 When the crisis started, it bore all the hallmarks of a coup. At the end, it almost resembled a popular revolt. "We think that this is the work of God," one young man told CNN in Harare. "We were in crisis for a long time, and this is a new day for Zimbabweans." 
 
 Key developments 
 
 Mugabe's letter: The ousted President insisted his resignation was voluntary. "I have resigned to allow smooth transfer of power," he wrote. "Kindly give public notice of my decision as soon as possible." 
 
 Successor lined up: Mnangagwa was the ZANU-PF's pick to succeed Mugabe, according to Simon Khaya Moyo, a spokesman for the ZANU-PF party. Mnangagwa will be sworn in within 48 hours of the Parliament speaker announcing Mugabe's resignation. 
 
 International reaction: Theresa May, the Prime Minister of Britain, from which Zimbabwe gained independence in 1980, said Mugabe's resignation provided the country "with an opportunity to forge a new path free of the oppression that characterized his rule." 
 
 Zimbabweans celebrate Robert Mugabe's resignation after 37 years of rule, in Harare on Tuesday. 
 
 What happened 
 
 Mugabe's announcement was an acknowledgment of the inevitable. In reality, he lost his grip on power six days ago when the country's top generals launched what amounted to a military coup, placing the veteran leader under house arrest. 
 
 The crisis began on November 6 when Mugabe fired Mnangagwa as vice president, in an apparent attempt to clear a path for his wife, Grace Mugabe, to succeed him. 
 
 Photos: Political upheaval grips Zimbabwe Members of Zimbabwe's Parliament celebrate after the resignation of longtime President Robert Mugabe was announced on Tuesday, November 21. Mugabe, 93, had led the country for nearly four decades. His resignation comes six days after military leaders seized control of the nation and placed him under house arrest. Hide Caption 1 of 35 Photos: Political upheaval grips Zimbabwe Protesters call for Mugabe's impeachment near the Parliament building in Harare on November 21. Hide Caption 2 of 35 Photos: Political upheaval grips Zimbabwe Demonstrators protest outside the Parliament building on November 21. Hide Caption 3 of 35 Photos: Political upheaval grips Zimbabwe Jacob Mudenda, the speaker of Zimbabwe's Parliament, presides over a session where a motion was moved to impeach Mugabe. Hide Caption 4 of 35 Photos: Political upheaval grips Zimbabwe A man accused of supporting Mugabe is attacked outside Parliament on November 21. Hide Caption 5 of 35 Photos: Political upheaval grips Zimbabwe People gather to pray for the country in a park near Parliament on November 21. Hide Caption 6 of 35 Photos: Political upheaval grips Zimbabwe Lawmakers meet inside Parliament on November 21. Hide Caption 7 of 35 Photos: Political upheaval grips Zimbabwe Gen. Constantino Chiwenga speaks during a news conference in Harare on Monday, November 20. Military leaders had been in talks with Mugabe over his exit, and Chiwenga said that progress had been made. Hide Caption 8 of 35 Photos: Political upheaval grips Zimbabwe Students from the University of Zimbabwe participate in a demonstration in Harare on November 20. Hide Caption 9 of 35 Photos: Political upheaval grips Zimbabwe Newspapers are held in place with rocks at a newsstand in Harare on November 20. Hide Caption 10 of 35 Photos: Political upheaval grips Zimbabwe At a bar in Harare, people watch Mugabe give a televised address to the nation on Sunday, November 19. Mugabe ended the address without giving his resignation. Hide Caption 11 of 35 Photos: Political upheaval grips Zimbabwe Mugabe meets with generals in Harare on November 19. Hide Caption 12 of 35 Photos: Political upheaval grips Zimbabwe Members of the ruling party ZANU-PF react after the decision to oust Mugabe as party leader on November 19. Hide Caption 13 of 35 Photos: Political upheaval grips Zimbabwe A portrait of Mugabe hangs in the hall of the ZANU-PF headquarters, where delegates met for a special committee on November 19. Mugabe co-founded the party and had been its leader for decades. Hide Caption 14 of 35 Photos: Political upheaval grips Zimbabwe A woman and her daughter look out from their balcony as a crowd of protesters gather on the road leading to the State House in Harare on Saturday, November 18. Hide Caption 15 of 35 Photos: Political upheaval grips Zimbabwe People hold a portrait of Zimbabwe's former vice president, Emmerson Mnangagwa, during a demonstration demanding Mugabe's resignation on November 18. ZANU-PF announced Mnangagwa as its new party leader. He was fired by Mugabe on November 6. Hide Caption 16 of 35 Photos: Political upheaval grips Zimbabwe A soldier greets a citizen during a demonstration on November 18. Hide Caption 17 of 35 Photos: Political upheaval grips Zimbabwe People in Harare react as they see a military helicopter fly overhead during protests against Mugabe on November 18. Hide Caption 18 of 35 Photos: Political upheaval grips Zimbabwe Mugabe, center, arrives to preside over a student graduation ceremony at Zimbabwe Open University on Friday, November 17. It was his first public appearance since the military takeover. Hide Caption 19 of 35 Photos: Political upheaval grips Zimbabwe Mugabe, right, is seen in talks about his future in this image tweeted by Caesar Zvayi, the editor of The Herald newspaper, on Thursday, November 16. Hide Caption 20 of 35 Photos: Political upheaval grips Zimbabwe An armored vehicle is on patrol in Harare on November 16. Hide Caption 21 of 35 Photos: Political upheaval grips Zimbabwe Business continues as usual in Harare as roadside vendors sell vegetables on November 16. Hide Caption 22 of 35 Photos: Political upheaval grips Zimbabwe Members of the military check a gun as they stand atop an armored vehicle parked in Harare's central district on November 16. Hide Caption 23 of 35 Photos: Political upheaval grips Zimbabwe An overview of Harare on November 16. Hide Caption 24 of 35 Photos: Political upheaval grips Zimbabwe A banner of Mugabe remains outside the ZANU-PF headquarters in Harare on November 16. Hide Caption 25 of 35 Photos: Political upheaval grips Zimbabwe An armored vehicle patrols a street in Harare on Wednesday, November 15. In a dramatic televised statement, an army spokesman denied that a military takeover was underway, but the situation bore all the hallmarks of one. The military said Mugabe and his family were "safe." Hide Caption 26 of 35 Photos: Political upheaval grips Zimbabwe Soldiers seal off a main road to the parliament building in Harare on November 15. Hide Caption 27 of 35 Photos: Political upheaval grips Zimbabwe Soldiers patrol a street in Harare on November 15. Hide Caption 28 of 35 Photos: Political upheaval grips Zimbabwe Soldiers inspect a vehicle on a road leading to Mugabe's office in Harare on November 15. Hide Caption 29 of 35 Photos: Political upheaval grips Zimbabwe Residents in Zimbabwe's capital line up to withdraw money from a bank on November 15. Hide Caption 30 of 35 Photos: Political upheaval grips Zimbabwe Two pedestrians pass behind an armored personnel carrier stationed at an intersection in Harare on November 15. Hide Caption 31 of 35 Photos: Political upheaval grips Zimbabwe A man in Harare reads a special edition of The Herald newspaper on November 15. Hide Caption 32 of 35 Photos: Political upheaval grips Zimbabwe An armored military vehicle is seen outside the building of the state-run Zimbabwe Broadcasting Corp. on November 15. Hide Caption 33 of 35 Photos: Political upheaval grips Zimbabwe Soldiers monitor traffic in Harare on November 15 as the military set up checkpoints at key locations in the city. Hide Caption 34 of 35 Photos: Political upheaval grips Zimbabwe In a screen grab of a TV broadcast on the Zimbabwe Broadcasting Corp., Maj. Gen. Sibusiso Moyo reads a statement saying the military was conducting an operation to target "criminals" close to the President who were causing "social and economic suffering." He denied a coup was underway. Hide Caption 35 of 35 
 
 Army generals and senior figures in Mugabe's ZANU-PF party, suspicious of the first lady's lavish lifestyle and political ambitions, were horrified by the possibility she could take over. 
 
 On Tuesday, tanks were seen outside Harare and in the early hours of Wednesday morning, an army spokesman appeared on state TV to declare that a military operation was underway. By dawn it was clear that Mugabe was under house arrest, and his grip on power ebbing away. 
 
 But Mugabe clung to power for a further six days, quitting only after his party ousted him as leader, and Parliament began impeachment proceedings. 
 
 The whereabouts of the former President and his wife were unknown on Tuesday. Grace Mugabe -- dubbed "Gucci Grace" for her penchant for extravagant shopping expeditions -- has not been seen since the day of the military takeover. Her husband's last appearance was during a television statement on Sunday night. 
 
 Zimbabweans raise their fists at the news of Robert Mugabe's resignation. 
 
 What comes next 
 
 ZANU-PF ousted Mugabe as leader of the party and installed Mnangagwa in his place on Sunday. 
 
 Emmerson Mnangagwa, left, served beside Robert Mugabe, right, throughout the leader's entire political career. 
 
 Mnangagwa has not been seen in the country since his dismissal on November 6, but he broke his silence on Tuesday to add his voice to those calling on Mugabe to resign. Mnangagwa, who enjoys widespread support in the military, was widely believed to be in touch with senior generals behind the scenes. 
 
 As Zimbabweans celebrated the demise of Mugabe on Tuesday, it was unclear whether they would welcome Mnangagwa. 
 
 Nicknamed "The Crocodile" for his political cunning and longevity, Mnanagagwa served as Mugabe's right-hand man for years. 
 
 He has been accused of orchestrating a string of massacres in the early 1980s to consolidate Mugabe's power, when he served as the leader's spy chief. The violence left up to 20,000 dead, mostly supporters of Mugabe's political opponents. Mnangagwa denies the allegations. 
 
 In late 2000, a cable written by a US diplomat in Harare, Earl Irving, described Mnangagwa as "widely feared and despised throughout the country," warning he could be "an even more repressive leader" than Mugabe if he were to succeed him. 
 
 End of an era 
 
 Photos: Political life and career of Robert Mugabe Robert Mugabe is sworn in for his seventh term as Zimbabwe's President in August 2013. He resigned Tuesday, November 21, after nearly four decades in power. Hide Caption 1 of 30 Photos: Political life and career of Robert Mugabe Mugabe gestures towards the media in Geneva, Switzerland, at a 1974 conference convened to address the civil war in Rhodesia. After being imprisoned for 10 years in Rhodesia, Mugabe attended the peace talks as a leader of the guerrilla movement ZANU-PF (Zimbabwe African National Union-Patriotic Front). Rhodesia was the state that eventually became Zimbabwe. Hide Caption 2 of 30 Photos: Political life and career of Robert Mugabe Mugabe speaks to the press in Geneva in 1976. The following year he was elected president of ZANU-PF and commander-in-chief of the Zimbabwe African National Liberation Army. Hide Caption 3 of 30 Photos: Political life and career of Robert Mugabe Mugabe holds a news conference in Salisbury -- now Harare, the capital of Zimbabwe -- in March 1980. He had just been elected as the first prime minister of Zimbabwe, helping to form the new country after British rule of Rhodesia came to an end. Hide Caption 4 of 30 Photos: Political life and career of Robert Mugabe From left, NBC News moderator Bill Monroe, Newsday's Les Payne, the Chicago Sun Times' Robert Novak and NBC News' Garrick Utley speak with Mugabe during an episode of "Meet the Press" in 1980. Hide Caption 5 of 30 Photos: Political life and career of Robert Mugabe Mugabe speaks with his first wife, Sally, during an event in Salisbury in 1980. The pair were married until Sally died in 1992. They had one son, who died at age 4. Hide Caption 6 of 30 Photos: Political life and career of Robert Mugabe Mugabe holds hands with Libyan leader Moammar Gadhafi at the Organization of African Unity summit in August 1982. Hide Caption 7 of 30 Photos: Political life and career of Robert Mugabe Mugabe meets with French President Francois Mitterand in Paris in 1982. Hide Caption 8 of 30 Photos: Political life and career of Robert Mugabe Mugabe is seen with Indian Prime Minister Indira Gandhi in New Delhi in 1983. Hide Caption 9 of 30 Photos: Political life and career of Robert Mugabe Mugabe walks hand in hand with American civil rights activist Jesse Jackson during the Summit of Non-Aligned Countries, which Harare hosted in 1986. Hide Caption 10 of 30 Photos: Political life and career of Robert Mugabe Mugabe delivers a speech in Harare in August 1986. Hide Caption 11 of 30 Photos: Political life and career of Robert Mugabe Mugabe poses for a photo with other leaders at a Commonwealth of Nations meeting in London in 1986. Pictured from left, in the back row, are Indian Prime Minister Rajiv Gandhi, Canadian Prime Minister Brian Mulroney, Commonwealth Secretary-General S.S. Ramphal, Australian Prime Minister Robert Hawke and Mugabe. In the front row, from left, are British Prime Minister Margaret Thatcher, Bahamian Prime Minister Lynden Pindling and Zambian President Kenneth Kaunda. Hide Caption 12 of 30 Photos: Political life and career of Robert Mugabe Britain's Queen Elizabeth II toasts Mugabe during a banquet in the Queen's honor in Harare in October 1991. The Queen had last visited the territory that became Zimbabwe in 1947. Hide Caption 13 of 30 Photos: Political life and career of Robert Mugabe US President Bill Clinton gestures while talking to Mugabe after a White House meeting in Washington in May 1995. Hide Caption 14 of 30 Photos: Political life and career of Robert Mugabe Mugabe marries Grace Marufu on August 17, 1996. Earlier in the year, he was re-elected President after all of his opponents dropped out of the race. Hide Caption 15 of 30 Photos: Political life and career of Robert Mugabe British Prime Minister Tony Blair talks with Mugabe in October 1997, before the start of the Commonwealth Heads of Government meeting. Hide Caption 16 of 30 Photos: Political life and career of Robert Mugabe Mugabe speaks during the Southern Africa trade and investment summit in Windhoek, Namibia, in October 2000. Earlier in the year, he implemented a controversial land-reform program that saw the seizure of land from some 4,000 white farmers. Hide Caption 17 of 30 Photos: Political life and career of Robert Mugabe Mugabe and Cuban President Fidel Castro are seen in Havana, Cuba, in September 2005. Hide Caption 18 of 30 Photos: Political life and career of Robert Mugabe South African President Jacob Zuma walks with Mugabe at Harare International Airport in March 2010. Hide Caption 19 of 30 Photos: Political life and career of Robert Mugabe Mugabe addresses the 65th session of the United Nations General Assembly in September 2010. Hide Caption 20 of 30 Photos: Political life and career of Robert Mugabe Mugabe cuts his birthday cake with his wife, Grace, and son Bellarmine Chatunga during celebrations in Harare in February 2011. Mugabe was turning 87. Hide Caption 21 of 30 Photos: Political life and career of Robert Mugabe Robert and Grace Mugabe arrive at the Vatican for the beatification ceremony of John Paul II in May 2011. Hide Caption 22 of 30 Photos: Political life and career of Robert Mugabe Mugabe delivers a speech at his party's annual national conference in December 2012. He vowed to overhaul business laws to require 100% black ownership of firms. Hide Caption 23 of 30 Photos: Political life and career of Robert Mugabe The Mugabes attend Pope Francis' inauguration Mass in March 2013. Hide Caption 24 of 30 Photos: Political life and career of Robert Mugabe Mugabe and Chinese President Xi Jinping participate in a signing ceremony in Beijing in 2014. Hide Caption 25 of 30 Photos: Political life and career of Robert Mugabe Mugabe speaks at the ZANU-PF party's annual conference in December 2016. The party endorsed Mugabe as its candidate for the 2018 election. Hide Caption 26 of 30 Photos: Political life and career of Robert Mugabe Mugabe reviews the guard of honor during Zimbabwe's 37th Independence Day celebrations in April 2017. Hide Caption 27 of 30 Photos: Political life and career of Robert Mugabe Mugabe kisses his wife during Independence Day celebrations in April 2017. In early November, the sacking of Mugabe's longtime ally and vice president, Emmerson Mnangagwa, was seen as a move to potentially clear the way for Grace Mugabe to succeed her 93-year-old husband. Hide Caption 28 of 30 Photos: Political life and career of Robert Mugabe Mugabe arrives to preside over a student graduation ceremony at Zimbabwe Open University in November 2017. It was his first public appearance since the military seized control of the nation and placed him under house arrest. Hide Caption 29 of 30 Photos: Political life and career of Robert Mugabe Mugabe meets with generals in Harare on November 19. Military leaders had been in talks with Mugabe over his exit. Hide Caption 30 of 30 
 
 Mugabe's resignation marks the end of an era in Zimbabwe. He ruled the country with an iron fist for almost four decades and is the only leader the nation has known since it achieved independence from Britain in 1980. 
 
 Mugabe's political demise is the consequence of a struggle over who would succeed him in ZANU-PF, a party split between those loyal to Mnangagwa and supporters of Grace Mugabe. 
 
 It was a humiliating departure for Mugabe, who clung onto power for a week but eventually buckled to pressure. 
 
 The party he co-founded to usher the country into independence ousted him, the military that he commanded placed him under house arrest and his most powerful allies abandoned him. 
 
 Mugabe rose to power as a freedom fighter and was once regarded as Zimbabwe's own Nelson Mandela. But he quickly waged a campaign of oppression to shore up his authority, extinguishing the political opposition through violent crackdowns. 
 
 Mugabe's hardline policies also pushed the country into poverty. Its flourishing economy began to disintegrate after a program of land seizures from white farmers, and agricultural output plummeted and inflation soared. 
 
 Over the decades, Mugabe and his wife faced fierce criticism for leading lavish lifestyles as the country was plunged into economic ruin. 
 
 The chairman of the African Union Commission said he welcomed Mugabe's decision to step down. 
 
 "Today's decision will go down in history as an act of statesmanship that can only bolster President Mugabe's political legacy," Moussa Faki Mahamat said in a statement. 
 
 "The African Union recognizes that the Zimbabwean people have expressed their will that there should be a peaceful transfer of power in a manner that secures the democratic future of their country. President Mugabe's decision to resign paves the way for a transition process, owned and led by the sovereign people of Zimbabwe." ||||| Demonstrators protest outside the Zimbabwean Parliament in Harare, Tuesday, Nov. 21, 2017 calling for Parliament to impeach President Robert Mugabe who has been in power for nearly four decades. Zimbabwean... (Associated Press) 
 
 HARARE, Zimbabwe (AP) — The Latest on Zimbabwe's political turmoil (all times local): 
 
 6 p.m. 
 
 Zimbabwe's President Robert Mugabe says he is resigning immediately and voluntarily in order to have a "smooth transfer of power" after 37 years in charge. 
 
 The letter was read out in a cheering, dancing Parliament, which had been pursuing impeachment of the 93-year-old Mugabe, the world's oldest head of state. 
 
 The resignation comes at the end of a week of extraordinary events that began with the military moving in last week, angered by Mugabe's firing of his longtime deputy and the positioning of the unpopular first lady to succeed him. 
 
 Impeachment allegations against Mugabe included that he "allowed his wife to usurp constitutional power" and that he is "of advanced age" and too incapacitated to rule. 
 
 Mugabe also was accused of allowing unpopular first lady Grace Mugabe to threaten to kill the recently fired Vice President Emmerson Mnangagwa and other officials. 
 
 ___ 
 
 5:55 p.m. 
 
 Zimbabwe's Parliament has erupted in cheers as the speaker announces the resignation of President Robert Mugabe. 
 
 The speaker stopped impeachment proceedings to say they had received a letter from Mugabe with the resignation "with immediate effect." 
 
 It is an extraordinary end for the world's oldest head of state after 37 years in power. 
 
 ___ 
 
 5:25 p.m. 
 
 An expert on Zimbabwean law says impeachment is a process that requires a vote, a committee investigation and a second vote. 
 
 Derek Matyszak, senior researcher for the Institute for Security Studies, says the first step is for both houses of Parliament to pass the impeachment motion by a 50 percent majority. Then a joint committee is formed to investigate allegations and determine if there is adequate evidence that Mugabe should be impeached. 
 
 If the committee recommends impeachment, both houses must pass the impeachment by a two-thirds majority, which is at least 233 seats of the 347-seat total. 
 
 Matyszak says that "the moment they vote to accept the report and impeach Mugabe, he loses office. The constitution is clear about that. Mugabe can appeal to the judiciary but he would be out of office." 
 
 It is not clear how long the process will take or how extensive the investigation would be, including with possible testimony from Mugabe. 
 
 Matyszak says that "I think it will be fast-tracked, but they want to take enough time to give the proceedings an air of propriety. They want this to look like a legitimate proceeding. That could be done so the final vote is on Wednesday or Thursday." 
 
 Parliament is currently hearing allegations and has not yet formed a committee. 
 
 ___ 
 
 5:15 p.m. 
 
 Zimbabwe's Parliament members are cheering as they listen to allegations against President Robert Mugabe as they enter the next stage of the impeachment process. 
 
 Parliament is now forming a committee to investigate the allegations against Mugabe, including that he "allowed his wife to usurp constitutional power" and that he is "of advanced age." 
 
 Mugabe also is accused of allowing unpopular first lady Grace Mugabe to threaten to kill the recently fired Vice President Emmerson Mnangagwa and other officials. 
 
 In addition, "we have seen the president sleeping in Cabinet and international meetings to the horror, shame and consternation of Zimbabweans." 
 
 The impeachment motion was introduced by the ruling party and seconded by the opposition MDC. It is not clear how long the process will take. 
 
 ___ 
 
 4:50 p.m. 
 
 Bells have rung to summon Zimbabwe's Parliament members to gather for the next stage of the impeachment process for President Robert Mugabe. 
 
 Parliament is now forming a committee to investigate the allegations against Mugabe, including that he "allowed his wife to usurp constitutional power" and that he is "of advanced age" and no longer has the physical capacity to run the government. 
 
 The impeachment motion was introduced by the ruling party and seconded by the opposition MDC. It is not clear how long the process will take, though lawmakers have said Mugabe could be voted out as early as Wednesday or Thursday. 
 
 ___ 
 
 3:45 p.m. 
 
 South Africa's state-run broadcaster reports that the presidents of South Africa and Angola will travel to Zimbabwe on Wednesday to meet with "stakeholders" in the political crisis, including President Robert Mugabe and the military. 
 
 Zimbabwe's Parliament has begun impeachment proceedings against Mugabe, who is accused of allowing his wife to "usurp" power and of being too old to rule. 
 
 It is not clear how long impeachment would take, though the ruling party has said it could vote Mugabe out as early as Wednesday. 
 
 South Africa, Angola and two other regional countries held a summit on the crisis Tuesday in Angola. 
 
 ___ 
 
 3:30 p.m. 
 
 Zimbabwe's ruling party has made a motion to impeach President Robert Mugabe and opposition party MDC has seconded it. 
 
 Now lawmakers from both houses of Parliament are relocating to a larger venue. 
 
 Mugabe is accused of allowing his wife to "usurp" power and of being too old to rule. He has been in charge since the end of white minority rule in 1980, but the military moved in last week after he fired his deputy and appeared to position his unpopular wife to succeed him. 
 
 It is not clear how long impeachment would take, though the ruling party has said it could vote Mugabe out as early as Wednesday. 
 
 ___ 
 
 3:10 p.m. 
 
 Zimbabwe opposition leader Morgan Tsvangirai is telling a crowd outside Parliament that a "democratic Zimbabwe cannot be built by another un-democratic process." 
 
 Tsvangirai says the culture of the ruling party "must end" and everyone must put their heads together and work toward free and fair elections. 
 
 "Now the question is, how do we end Mugabe," says the opposition leader, who shared power with Mugabe as prime minister for a number of years. 
 
 ___ 
 
 2:45 p.m. 
 
 Parliament has opened in Zimbabwe as the ruling party seeks to impeach President Robert Mugabe after nearly four decades in power. 
 
 Mugabe is accused of allowing his wife to "usurp" power and of being too old to rule. 
 
 Mugabe has been in charge since the end of white minority rule in 1980, but the military moved in last week after he fired his deputy and appeared to position his unpopular wife to succeed him. 
 
 Zimbabweans are rallying outside Parliament. It is not clear how long impeachment would take, though the ruling party has said it could vote Mugabe out as early as Wednesday. 
 
 ___ 
 
 2:20 p.m. 
 
 Zimbabweans are rallying outside Parliament as the ruling party is poised to begin impeachment proceedings against President Robert Mugabe, who is accused of allowing his wife to "usurp" power and of being too old to rule. 
 
 "We are here because we want to be part of this very important occasion in the history of this country," says Harare resident Samuel Wadzai. 
 
 Lawmakers have begun arriving at Parliament. 
 
 Mugabe has been in power since the end of white minority rule in 1980, but the military moved in last week after he fired his deputy and appeared to position his unpopular wife to succeed him. 
 
 The pastor who last year led the country's largest anti-government protests in a decade, Evan Mawarire, tells the crowd that "our country was a shame and we were embarrassed by it. But today we declare that we love Zimbabwe." 
 
 ___ 
 
 2 p.m. 
 
 Botswana's government has posted online what it calls an open letter from President Ian Khama urging Zimbabwe President Robert Mugabe to step down. 
 
 Khama has openly criticized his neighbor in the past. His letter posted on social media comes as Zimbabwe's ruling party is poised to begin impeachment proceedings against Mugabe. 
 
 The letter asks the world's oldest head of state to "be sensitive to the wishes of the people of Zimbabwe and to do the honourable thing by voluntarily relinquishing power." 
 
 Khama adds that Zimbabwe's people have been "subjected to untold suffering" under Mugabe, who has ruled for 37 years while the once-prosperous southern African nation's economy collapsed. 
 
 ___ 
 
 12:50 p.m. 
 
 A Zimbabwean ruling party senior official says Cabinet ministers have snubbed a call by President Robert Mugabe to attend a meeting. 
 
 Lovemore Matuke says "all" ministers heeded a party directive to skip the Cabinet meeting and instead attend a party caucus to discuss impeaching Mugabe. 
 
 The party's Central Committee has voted to strip Mugabe of his party leadership post amid nationwide calls for the 93-year-old leader to resign. Mugabe, however, says he plans to preside over a ruling party congress next month. 
 
 The ruling party is poised to begin impeachment proceedings against Mugabe on Tuesday. 
 
 ___ 
 
 10:25 a.m. 
 
 Four regional countries are meeting on Zimbabwe's political crisis. 
 
 South Africa's president is joining the Angola-hosted summit of the Southern African Development Community, along with the leaders of Zambia and Tanzania. 
 
 A committee of the regional bloc has recommended a full summit of all 16 members to discuss Zimbabwe, where longtime President Robert Mugabe faces impeachment after his firing of his deputy and positioning of the unpopular first lady to succeed him. 
 
 ___ 
 
 9:45 a.m. 
 
 The Zimbabwe vice president whose firing kicked off the country's political crisis says President Robert should heed the "clarion call" and resign immediately: "The people of Zimbabwe have clearly spoken." 
 
 The new statement from Emmerson Mnangagwa makes clear that he remains outside Zimbabwe after fleeing and won't return until his security is guaranteed. 
 
 Mnangagwa confirms that Mugabe has invited him to return "for a discussion" on the recent events. But "given the events that followed my dismissal I cannot trust my life in President Mugabe's hands." 
 
 He says his security was withdrawn upon his firing and he was informed that "plans were underfoot to eliminate me once arrested." 
 
 Mnangagwa says he is aware of the impeachment proceedings that start Tuesday against Mugabe and "I will not stand in the way of the people and my party." 
 
 ___ 
 
 9:20 a.m. 
 
 A recently fired Zimbabwean vice president and likely successor to President Robert Mugabe says the 93-year-old leader should resign immediately. 
 
 Emmerson Mnangagwa says in a statement Tuesday that he is not in Zimbabwe and that he would not return to the country until he is "satisfied of my personal security." 
 
 Mugabe fired Mnangagwa earlier this month, but Zimbabwe's ruling party is demanding that Mugabe resign and wants the former vice president to replace him. 
 
 The ruling party is poised to begin impeachment proceedings against Mugabe on Tuesday as Parliament resumes, and it has instructed government ministers to boycott a Cabinet meeting Mugabe has called for Tuesday morning. 
 
 ___ 
 
 9 a.m. 
 
 Zimbabwe's ruling party is set to begin impeachment proceedings against longtime President Robert Mugabe, while a party official says government ministers have been instructed to boycott a Cabinet meeting called by the president. 
 
 Ruling party chief whip Lovemore Matuke tells The Associated Press minutes before the Cabinet meeting is expected to start that ministers have been told to instead attend a meeting at party headquarters to work on the impeachment. Parliament resumes Tuesday. 
 
 Mugabe's chief secretary on Monday summoned ministers to the Cabinet meeting at State House, the president's official residence. 
 
 Mugabe is finding himself increasingly isolated. 
 
 The military on Monday night said the vice president he recently fired, sparking the political turmoil, will return to Zimbabwe "shortly" and has made contact with Mugabe.
– Zimbabwe's President Robert Mugabe says he is resigning immediately and voluntarily in order to have a "smooth transfer of power" after 37 years in charge. The news came via a letter that was read out to a cheering, dancing parliament, which had been pursuing impeachment of the 93-year-old Mugabe, the world's oldest head of state, reports the AP. How big a deal is this? CNN provides context: Zimbabwe got its independence from Britain in 1980, and Mugabe has been the only ruler the people have had that entire time; he had vowed to rule until his death. USA Today reports that citizens put photos of Mugabe in the street to be run over by cars. More: Background: The resignation comes at the end of a week of extraordinary events that began with the military moving in last week, angered by Mugabe's firing of his longtime deputy and the positioning of the unpopular first lady to succeed him. Impeachment allegations against Mugabe included that he "allowed his wife to usurp constitutional power" and that he is "of advanced age" and too incapacitated to rule. Mugabe also was accused of allowing first lady Grace Mugabe to threaten to kill the recently fired Vice President Emmerson Mnangagwa and other officials.