U.S. Army soldiers take up a position during a patrol in Baghdad in 2007. The U.S. has been waging war nonstop for 15 years since the Sept. 11 attacks. Despite the protracted conflicts and disappointing results, U.S. involvement in multiple wars appears set to continue for years to come.
Joe Raedle/Getty Images
Al-Qaida leader Osama bin Laden speaks to a selected group of reporters in the mountains of Helmand province in southern Afghanistan in 1998. It has been five years since he was killed in a U.S. raid in Pakistan.
Handout picture dated 1997 and released in 2012 by the UN shows ancient manuscripts displayed at the library in the city of Timbuktu. Al-Qaeda has destroyed ancient texts it considers idolatrous.
Evan Schneider/AFP/Getty Images
Salimata Sylla, a mother of three, visits Grand Bassam with her family to show she's not afraid of terrorists. On March 13, al-Qaida gunmen killed some 19 people at the beachfront town.
A screenshot of Lucas Kinney, a 26-year-old Briton who recently began making videos for Jabhat al-Nusra, the al-Qaida affiliate in Syria. Kinney's father is a veteran Hollywood assistant director who helped make such films as Rambo and the Indiana Jones series.
A 1998 file photo of Ayman al-Zawahri speaking at a news conference in Khost, Afghanistan. The reclusive al-Qaida leader says he has pledged support to the new chief of the Taliban, Mullah Akhtar Mansoor.
Mazhar Ali Khan/AP
An undated file picture shows Osama bin Laden. A new Wikileaks release purports to reveal that one of his sons requested a death certificate for the al-Qaida leader, who was killed in a U.S. military raid in 2011.
An image of Mokhtar Belmokhtar from the U.S. State Department's wanted poster in the Rewards for Justice program. Belmokhtar was a leading figure in al-Qaida in the Islamic Maghreb.
U.S. Department of State
An Islamic State fighter holds holds a rifle and the group's flag shortly after capturing the northern Iraqi city of Mosul in June 2014. Dozens of Americans have been accused of planning or heading off to the Middle East to join the group. Their individual cases are on the chart below.