Al Qaida is one of a number of extremist groups that originated during or immediately after the Soviet-Afghan war (1979-1989). It was founded by Usama bin Laden, a wealthy Saudi with extreme political and religious views. He played a prominent part in the international Islamic movement that supported anti-Soviet guerrillas in Afghanistan. Following the Afghan war, bin Laden drew together a group of like-minded extremists to establish a "base" or "foundation" (in Arabic, "al Qaida") to support extremist causes elsewhere.

After the Soviet withdrawal from Afghanistan in 1989, many foreign fighters returned to their home countries or moved on to other areas of conflict around the world. This led to an upsurge of violence across the Middle East, North Africa and South Asia in the 1990s as extremists sought to overthrow governments or supported ongoing separatist conflicts such as in Kashmir and Chechnya.

While most extremist groups focused on regional governments, which they regarded as the "near enemy", bin Laden concentrated on the "far enemy" - the West, and specifically the United States - which he held responsible for the problems of the Islamic world. In 1992, the Al Qaida leadership published a fatwa or religious decree calling for jihad (holy war) against the Western presence in the Middle East, singling out United States forces as a target. This theme was further developed in another fatwa issued in August 1996, "Declaration of War Against the Americans Occupying the Land of the Two Holy Places" [i.e. Saudi Arabia]. Later Al Qaida statements have singled out a number of countries, including the UK, as "enemies".

Al Qaida carried out a number of terrorist attacks following its 1996 declaration. The bombings of the US embassies in Kenya and Tanzania in August 1998 and the attack on the USS Cole off the coast of Yemen in October 2000 killed over 270 people and injured 5,000 more. These attacks provided early demonstrations of one of Al Qaida's signature methods: the use of large bombs detonated by suicide bombers, causing indiscriminate destruction and mass civilian casualties.

The 11 September 2001 attacks in the United States showed Al Qaida's desire for "high impact" attacks with a worldwide resonance and its indifference to causing mass civilian casualties of any background or religion. Nearly 3,000 people were killed in the attacks, with at least another 6,000 reported to have been injured.

In the aftermath of the 9/11 attacks, international military action in Afghanistan overthrew Al Qaida's Taliban allies, deprived Al Qaida of much of its infrastructure and forced the leadership, including Usama bin Laden himself, to flee into the Pakistan/Afghanistan borderlands. The international community also undertook a major crackdown on terrorist financing, seriously obstructing Al Qaida's access to funds. These actions significantly disrupted the organisation and forced it to decentralise its operations.

However, the attacks in the United States had a number of positive benefits for Al Qaida. The success of the attacks raised the group's profile greatly, boosting its appeal to potential supporters and bringing its ideology to worldwide attention. These factors contributed to a widespread worldwide resurgence of terrorist activity. The number of extremist groups and individuals involved in them has increased considerably since 2001. Terrorist groups have become increasingly active across the Middle East and in a number of European countries, including the UK.
The core Al Qaida leadership remains at large and has exploited fresh opportunities to attract new recruits and promote its cause more widely. Groups affiliated to or inspired by Al Qaida are also continuing to carry out terrorist activities in many countries around the world.