Experts argue that this restructured al-Qaida is perhaps even stronger than it has been in recent years, and that the potential for attacks on U.S. soil endures.
"We have never been on a path to strategically defeat al-Qaida. All we've been able to do is suppress some of its tactical abilities. But strategically, we have never had an effective way of taking it on. That's why it continues to mutate, adapt and evolve to get stronger," said David Sedney, former deputy assistant secretary of defense for Afghanistan, Pakistan and Central Asia.
Decentralization does not mean weakness, he said.
"I think Americans think al-Qaida is no longer a threat — that Osama bin Laden's death means al-Qaida is not a big thing anymore," Sedney said.
He believes al-Qaida is gaining strength in Pakistan, is stronger in Iraq than it was three or four years ago and is stronger in Syria than it was a year or two ago.
"This is a fight about ideology. Al-Qaida is not this leader or that leader or this group or that group," he said.
The experts say al-Qaida today looks less like a wheel with spokes and more like a spider web stringing together like-minded groups. But they believe there are several reasons that those who track al-Qaida warn against complacency.
While bin Laden was killed and his leadership team heavily damaged by U.S. drone strikes in Pakistan, the drawdown of American forces in neighboring Afghanistan will dry up field intelligence and restrict the effectiveness of U.S. counterterrorism operations. There is a worry that a pullback could allow al-Qaida to regroup.
Moreover, they worry about the thousands of foreign fighters flocking to the civil war in Syria, which has emboldened the al-Qaida breakaway group known as the Islamic State of Iraq and the Levant to expand its cross-border operations into neighboring countries such as Iraq.
U.S. officials also are concerned about Westerners who have joined the Syrian fight because they may be recruited to return home and conduct attacks.
When the U.S. counterterrorism strategy was conceived, it was thought that if al-Qaeda's core leadership was dismantled or killed, then affiliated groups would simply become localized threats, said Katherine Zimmerman of the conservative American Enterprise Institute.
At that time, there wasn't a network of connections among all the groups, said Zimmerman, who specializes in the Yemen-based group, Al-Qaida in the Arabian Peninsula, or AQAP, and al-Qaida's affiliate in Somalia, al-Shabab.
"As the network has become more decentralized, it's become much more reliant on these human relationships and the sharing of resources, advice and fighters, which means that you no longer need bin Laden sitting in Pakistan dispersing cash to various affiliates," Zimmerman said. "They have developed their own sources. ... You can't simply pound on part of the network and expect to see results."
Tom Joscelyn, a senior fellow at the Foundation for Defense of Democracies and senior editor of The Long War Journal, a website that tracks how al-Qaida and its affiliates operate around the globe, said he thinks the Bush and Obama administrations mistakenly defined al-Qaida as a top-down pyramid with a hierarchal structure — that "if you sort of lop off the top of the pyramid, the whole thing crumbles."
Al-Qaida leaders have scattered to other parts of the world, he said, noting that Al-Qaida in the Arabian Peninsula is headed by a former aide to bin Laden, who is now general manager of al-Qaida globally.