As the Saudi-led military intervention in Yemen escalated in July 2015 , 50 civilians were killed , and 20 million were in need of aid . In February 2016 , al-Qaeda forces and Saudi Arabian-led coalition forces were both seen fighting Houthi rebels in the same battle . In August 2018 , '' Al Jazeera '' reported that " A military coalition battling Houthi rebels secured secret deals with al-Qaeda in Yemen and recruited hundreds of the group 's fighters . ... Key figures in the deal-making said the United States was aware of the arrangements and held off on drone attacks against the armed group , which was created by Osama bin Laden in 1988 . " In December 1998 , the Director of the CIA Counterterrorism Center reported to President Bill Clinton that al-Qaeda was preparing to launch attacks in the United States , and that the group was training personnel to hijack aircraft . On September 11 , 2001 , al-Qaeda attacked the United States , hijacking four airliners within the country and deliberately crashing two into the twin towers of the World Trade Center in New York City . The third plane crashed into the western side of the Pentagon in Arlington County , Virginia . The fourth plane was crashed into a field in Shanksville , Pennsylvania . In total , the attackers killed 2,977 victims and injured more than 6,000 others
attacked the United States
September 11 attacks
Al-Qaeda