Since Islamic State fighters entered Iraq from Syria , they have given the world a revolting look at their ruthlessness . They have left the severed heads of their vanquished on spikes . They have filled mass graves with the summarily executed . They have slaughtered and enslaved ethnic minority Yazidis . When the Islamic State drove tens of thousands of them up mountains , where many died of thirst , it seemed the last straw . U.S. President Barack Obama ordered airstrikes to beat them back . But the same cruelty has fumed next door in Syria -- along with the atrocities committed by forces loyal to President Bashar al-Assad against rebel fighters . While the world focused on the plight of the Yazidis in Iraq , 500 Syrian civilians died practically unnoticed . So , why is the United States intervening in Iraq , while avoiding Syria ? The answers lie in some clear differences in the two conflicts : . 1. International opposition . No nation protects Islamic State . Even al Qaeda is disgusted by its viciousness . But international political entanglement awaits any power pondering action in Syria , due to loyalties to al-Assad . As the United States and its allies have called for action against his regime , China and Russia have put their foot down in the UN Security Council . And Russia has kept al-Assad well-armed . Although Russia rails against Muslim extremists , a U.S. intervention -- even only against Islamic State -- would meet with deep distrust in the Kremlin , especially after the relationship with Washington hit the dustbin over Ukraine . Iran , a close al-Assad ally , would likely also be up in arms . Tehran is allegedly supplying Shia militia Hezbollah , which has crossed from Lebanon to shore up al-Assad 's troops . 2 . Confusing battlefield . Syria 's war is a checkerboard battle -- government troops and Hezbollah in a fight against Islamic State and other resistance groups , who also battle each other . Obama does n't see a strong partner in the politically fractured Free Syrian Army , because it 's hardly a formidable force against al-Assad 's professional army . In Iraq , the battle lines are clearer -- the Iraqi government with U.S. support vs. Islamic State . Baghdad has made a shaky showing against the militants . But in the north , Washington has a strong , loyal partner in semi-autonomous Kurdistan . Many of the U.S. advisers deployed to Iraq are stationed in its capital Irbil to support Peshmerga troops in hot confrontation with Islamic state . 3 . Ineffective airstrikes . The Syrian government has professional air defenses , including its own air force , which would give the U.S. military serious resistance . Though Islamic State has struck some aircraft , its air defenses are flimsy when compared to al-Assad 's . The Iraqi government was bombing Islamic State long before U.S. drones and warplanes joined them , and the Kurdish government has begged for U.S. air support . President Obama has approved targeted strikes in Iraq , but his hawkish critics in Washington have called for much tougher U.S. military action against the Islamist extremists . 4 . We broke it . We fix it . It 's a moan often heard in the United States these days . Iraq would not be in this predicament , had U.S. forces not invaded and destabilized it . Morally , the country owes them . Add to that the American and civilian lives lost in the war to depose former dictator Saddam Hussein , the hundreds of billions spent , the training and arming of Iraqi forces . The U.S. has no such vested interest in Syria . But , says CNN analyst Fareed Zakaria , that 's a stance Washington ca n't afford to maintain . `` The United States should develop a more cogent and integrated policy approach that deals with Syria and Iraq together -- the challenges in both countries are becoming more interlinked , '' he said . 5 . A wariness to step in . To be sure , the President 's stance has its critics . Republican Senators John McCain and Lindsey Graham want Obama to take the fight against Islamic State into Syria . Respect for its borders take a back seat to stopping the extremists , they say . Former U.S . Ambassador to Syria Robert Ford resigned in protest of America 's inaction against al-Assad . He has found fault with Washington for allowing Islamic State to burgeon in Syria . And former Secretary of State Hillary Clinton recently said that the President does not apply U.S. might aggressively enough . But , after pulling the country out of two wars in Afghanistan and Iraq , the President has said that the United States should be leery of trying to solve the world 's crisis . As he has reportedly said , `` Do n't do stupid stuff . '' How religion could complicate U.S. intervention in Iraq . Opinion : What the U.S. can realistically do in Iraq .
" State terrorism has fumed in Syria , too , along with other atrocities . But complex entanglements would make it more difficult to survive there than in Iraq . In Syria , the government would fight against the rebels ; in Iraq they are not .