The killing of Osama bin Laden is undoubtedly a triumph for the administration of the US president Barack Obama. But as the president himself has recognised, it does not mean the end of al Qa'eda, which will remain among the most serious security threats to the United States and its allies.
Osama bin Laden: Complete coverage of the killing of the world's most wanted terrorist.
Last Updated: May 3, 2010
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Nearly a decade after the September 11 attacks on the United States, al Qa'eda has transformed itself from a centralised group to a brand name used by assorted jihadist movements across the globe. The organisation founded by bin Laden in the 1980s has morphed into small, localised cells and affiliated groups that do not necessarily take orders from the old leadership. But it is clear they have been inspired, if not specifically directed, by bin Laden.
Al Qa'eda and its offshoots have carried out smaller-scale attacks including the March 2004 bombings of four commuter trains in Madrid and the July 2005 transit bombings in London. Today, perhaps the most dangerous affiliate is al Qa'eda in the Arabian Peninsula, which has claimed responsibility for a series of near-miss attacks on the United States, including the attempted bombing of a Detroit-bound airliner on Christmas Day 2009.
One of the group's leaders is Anwar al Awlaki, an American-born cleric who now lives in hiding in Yemen. His stature within al Qa'eda is likely to rise as militants seek other charismatic figures to pick up bin Laden's mantle.
In announcing bin Laden's death on Sunday evening, Mr Obama warned that al Qa'eda remains active and the US could face retaliation. "There is no doubt that al Qa'eda will continue to pursue attacks against us," Mr Obama said. "We must and we will remain vigilant at home and abroad."
When the United States invaded Afghanistan in October 2001 to drive out the ruling Taliban movement that sheltered bin Laden and his deputies, al Qa'eda was temporarily thrown off balance. But it quickly regrouped, dispersing its surviving members, distributing its ideological tracts and terrorist techniques to a wider audience on the internet and encouraging new recruits to act autonomously under its banner.
This transformation - from a hierarchical group toward an amorphous network that provides ideological direction and tactical support - was hinted at by bin Laden from the time he founded al Qa'eda (Arabic for "the base") in the rugged Afghan mountains in 1988. In his speeches and statements, bin Laden framed his legacy as that of an historic leader who would inspire the world's Muslims to rise up against US dominance in the Middle East. But his message of hatred and violence did not take hold among the vast majority of Muslims, especially after al Qa'eda affiliates began killing large numbers of civilians in Iraq.
Even while in hiding, bin Laden and his top lieutenant, Ayman al Zawahiri, freely addressed their supporters through dozens of videos, audiotapes and internet statements. They helped inspire hundreds of young men to carry out suicide or conventional bombings in Iraq, Saudi Arabia, Egypt, Jordan, Morocco, Spain, Turkey and Britain.
Bin Laden and al Zawahiri were believed to be hiding in mountainous areas along the Afghanistan-Pakistan border, under the protection of ethnic Pashtun tribes. They knew the area well, having fought there in the 1980s during the CIA-sponsored jihad against the Soviet occupation of Afghanistan. But bin Laden was found and killed in a Pakistani city about an hour's drive north of Islamabad, the capital. In the coming days, Pakistani leaders will face questions about how bin Laden managed to elude them for so long and how al Qa'eda was able to rebuild its infrastructure in the tribal region of northwest Pakistan.
It is unclear how many of bin Laden's original followers - several thousand veterans of the Afghan jihad who joined al Qa'eda or went through its training camps in the 1990s - are at large. Many veterans of the Afghan war went on to fight and die in Bosnia, Chechnya and elsewhere. Hundreds were detained in their home countries. And an unknown number have been killed or captured by the United States.
While they might act independently, offshoot groups choose their targets based on al Qa'eda's political priorities. In a series of letters and taped messages over the past 10 years, bin Laden and al Zawahiri provided their followers with a framework for carrying out new attacks. They urged strikes against US interests and any other country with troops in Iraq or Afghanistan. They recommended attacking soft targets that have economic importance, such as mass transit systems, and timing attacks to coincide with key political events.
The Madrid and London attacks fit into bin Laden's call for adherents to strike at US allies. The new recruits adopted al Qa'eda's hallmark method: simultaneous bombings against political or economic soft targets, designed to inflict heavy casualties and spread fear. Al Qa'eda affiliates also worked to disseminate expertise to make deadlier explosives by training a small number of people who could then teach others, often through the internet.
This generation of young recruits is less connected to the traditional al Qa'eda leadership, and many of its members come together through the internet. Before the September 11 attacks, bin Laden had relied on recruits trained at Afghan camps, and many had personally pledged allegiance to him.
But in recent years bin Laden was much more of a symbol and a source of ideology than a planner of specific attacks. One of bin Laden's former bodyguards in Afghanistan once described the group's operations to an Arabic newspaper: "Every element of al Qa'eda is self-activated. Whoever finds a chance to attack simply goes ahead. The decision is theirs alone."
In the short term at least, bin Laden's death is more likely to result in retaliatory attacks than to further disrupt al Qa'eda's actions.
Mohamad Bazzi is a journalism professor at New York University and an adjunct senior fellow at the Council on Foreign Relations