The killing of Osama bin Laden marks the culmination of a counterterrorism campaign that made decapitating the al Qaeda network its paramount goal.
But al Qaeda has metastasised in the decade since the September 11, 2001, attacks, expanding its reach and adapting its tactics in ways that make the organisation likely to remain the most significant security threat to the United States despite its leader's demise.
In recent months, the top US intelligence officials have testified that al Qaeda's affiliate in Yemen probably poses the most immediate threat to US interests.
Al Qaeda has established ties to militant movements in other countries, such as Somalia.
And even in Pakistan, where bin Laden was killed, the terrorist group functions in some ways as a force multiplier for other militant organisations, including the Afghanistan Taliban.
President Obama acknowledged in his late-night speech Sunday that bin Laden's death did not mark the end of the al Qaeda threat.
"There is no doubt al Qaeda will continue to pursue attacks against us," Obama said.
"We must, and we will remain, vigilant at home and abroad."
Experts said that bin Laden in recent years had served much more as a symbol than as an operational figure, and that the implications of his death for al Qaeda are not entirely clear.
Retired CIA veteran, Paul Pillar, said al Qaeda has been widely decentralised, spreading to Yemen-based al Qaeda in the Arabian Peninsula and other organisations, and that bin Laden's death would have little impact on the planning of attacks.
"In terms of operational control and direction, most of the change that matters has already taken place," he said.
Bin Laden's role "for some time has been more as a symbol and a source of ideology than an instigator of operations. That role will continue, dead as well as alive."
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