For the most part, al-Qaida's regional power centers have formed in places undergoing political upheaval, where security forces are too distracted by internal war or strife to clamp down on extremists.
The civil war in Syria, now in its third year, has given al-Qaida a huge boost and an opportunity to seize land that the Sunni-based network has long yearned to control. Having a leadership role in Syria would be a victory for al-Qaida given the country's prominence in Muslim scripture, its proximity to other Arab states and the network's hatred toward Alawites, an offshoot of Shiite Islam, who include Syrian President Bashar Assad.
More than 100,000 people have died in the Syrian war, which largely pits Sunni opposition forces and rebels against Assad's Alawite regime, and has drawn fighters linked to al-Qaida. Many have come from neighboring Iraq, which itself is reeling from political instability.
Violence has risen steadily since the American military left Iraq in December 2011, fueled in part by Syrian cross-border militant traffic but also because of Baghdad's inability to curb attacks.
July was the deadliest month in Iraq in years, with attacks killing more than 1,000 people and wounding at least 2,300, according to U.N. data. And coordinated jailbreaks at two high-security Iraqi prisons last month set free hundreds of inmates, including al-Qaida extremists. Iraq's branch of al-Qaida, known as the Islamic State of Iraq and the Levant, claimed responsibility for the raids that it said were planned for months.
Kenneth Pollack, who oversaw Persian Gulf issues while on the White House National Security Council during the Clinton administration, said al-Qaida is poised to gain from instability across the Mideast - in part by using Iraq as a regional hub.
"Al-Qaida in Iraq is back. They were dead in 2010, dead as doornails, and now they are huge in Iraq," Pollack said. "They have operations in Syria and they are a real movement in Syria."
But the al-Qaida fighters in Iraq and Syria have shown little interest in attacking Americans beyond the region, Pollack said, and neither have most of those in northern Africa. There, in a region that spans across the Sahel and stretches from the Mediterranean Sea to Somalia, a spread of militants are calling themselves al-Qaida in Islamic Maghreb.
AQIM is rooted in Algeria and affiliated with al-Zawahri, who in April warned French troops fighting extremists in Mali that they would face "the same fate America met in Iraq and Afghanistan" as long as they stayed. But there's no evidence the North African groups receive direct orders from al-Zawahri, and most are as motivated by asserting local authority through criminal activity as by anti-Western ideology.
It's believed that AQIM was linked to some of the militants behind last year's attack on a diplomatic post in Benghazi, Libya, that killed Ambassador Chris Stevens and three other Americans. And AQIM is suspected of driving overloaded trucks of rifles, mortars and other weapons from Libya to Mali and Niger to arm allies there.
Al-Zawahri also urged Muslims to join Somali militants in a message last November. The Somali-based militant group al-Shabab is loosely linked to al-Qaida, but some of its members have plotted attacks against the United States, where large pockets of Somalis have moved to escape famine and war over the last 20 years.
An inevitable part of al-Qaida's growth is its new regional leadership - few of whom fought with bin Laden or have ever worked with al-Zawahri, Katz said. They may not all be driven by the same anti-American or anti-Western fervors that motivated bin Laden, but that makes them no less a global threat as the disparate groups mature.
"In the past, people wanted to go to Afghanistan; it was the dream of every possible jihadi on the front to go to Afghanistan to fight in al-Qaida training camps," Katz said. "You don't see that anymore. No one cares about what's happening in Afghanistan.
"If anyone wants to go anywhere today it is, of course, Syria," she said. "Going to Yemen is always a good thing for them; going to Somalia is less than it used to be, but it's still another possibility. Things change all the time."