Bin Laden’s demise is a defining moment in the American-led fight against terrorism, a symbolic stroke affirming the relentlessness of the pursuit of those who attacked New York and Washington on Sept. 11, 2001. What remains to be seen, however, is whether it galvanizes Bin Laden’s followers by turning him into a martyr or serves as a turning of the page in the war in Afghanistan and gives further impetus to Mr. Obama to bring American troops home.

How much his death will affect Al Qaeda itself remains unclear. For years, as they failed to find him, American leaders have said that he was more symbolically important than operationally significant because he was on the run and hindered in any meaningful leadership role. Yet he remained the most potent face of terrorism around the world, and some of those who played down his role in recent years nonetheless celebrated his death.

Given Bin Laden’s status among radicals, the American government braced for possible retaliation. A senior Pentagon official said late Sunday that military bases in the United States and around the world were ordered to a higher state of readiness. The State Department issued a worldwide travel warning, urging Americans in volatile areas “to limit their travel outside of their homes and hotels and avoid mass gatherings and demonstrations.”

The strike could deepen tensions with Pakistan, which has periodically bristled at American counterterrorism efforts even as Bin Laden evidently found safe refuge on its territory for nearly a decade. Since taking office, Mr. Obama has ordered significantly more drone strikes on suspected terrorist targets in Pakistan, stirring public anger there and prompting the Pakistani government to protest.

When the end came for Bin Laden, he was found not in the remote tribal areas along the Pakistani-Afghan border where he has long been presumed to be sheltered, but in a massive compound about an hour’s drive north from the Pakistani capital of Islamabad. He was hiding in the medium-sized city of Abbottabad, home to a large Pakistani military base and a military academy of the Pakistani Army.