On September 11, 2001, 19 al-Qaeda hijackers took control of 4 commercial airliners, crashing two planes into the World Trade Center towers, one into the Pentagon, and one crashed in Pennsylvania; over 2,600 people were killed during the 9/11 terrorist attacks planned by al-Qaeda leader Osama bin Laden in response to U.S. support of Israel and deployment of troops in Saudi Arabia.