Correction: An earlier version of this analysis referred to Osama bin Laden as “Obama” in a reference to President George W. Bush’s statement after the Sept. 11, 2001, attacks that he wanted the al-Qaeda leader captured “dead or alive.” This version has been corrected.

President Obama’s historic announcement late Sunday night that Osama bin Laden is dead represents a huge national security victory for the United States and a milestone for this administration, bringing to a close the most relentless mission by U.S. intelligence and military forces over the past 10 years.

Obama’s announcement, which came just before midnight, was grounds for celebration for a country still scarred by the attacks of Sept. 11, 2001, producing a rare moment of national unity at a time of deep divisions on many domestic and foreign policy issues.

The spontaneous flag-waving crowds that gathered outside the White House, cheering and singing the national anthem and “God Bless America” were a small symbol of the emotional relief that swept across the country as the news broke late in the evening.

Bin Laden’s death will not end the threat posed by al-Qaeda to the United States and other parts of the world. But the demise of the person most responsible for the attacks on Sept. 11, which killed about 3,000 people represents a major psychological setback to the terrorist organization and a sizable boost for the president and the country.

“Justice has been done,” the president said in a nationally televised statement to the nation.

There have been other victories over the past decade as U.S. intelligence officials have pursued and killed other top members of the al-Qaeda organization. But nothing compares in significance to the declaration Obama was able to make Sunday night. As the president put it, the killing of bin Laden marks “the most significant achievement to date in our efforts to defeat al-Qaeda.”

Bin Laden came to symbolize the insidious threat of non-state terrorism that has been a defining feature of the 21st century. The attacks that leveled the World Trade Center, demolished a portion of the Pentagon and that killed more people when another hijacked plane crashed in western Pennsylvania reshaped the daily lives of all Americans, symbolized by heightened security at every airport and the huge homeland security network that has been built over the past decade.

That won’t change with bin Laden’s death, as the threat of terrorist attack, from al-Qaeda and its offshoots, remains strong. But it will underscore the reality of the commitment of this administration, as with the administration of former president George W. Bush, to try to hunt down and kill those responsible.

Bush put down the marker not long after the Sept. 11 attacks, saying he wanted bin Laden “dead or alive.” That was taken as a sign of cowboy swagger by a Texan president by some of his critics, but it was a reflection of the absolute importance that he and much of the nation attached to bringing to justice the man responsible for the worst terrorist attack on the homeland in the history of the nation.

The terrorist leader was nearly captured in Afghanistan early in the war there but managed to slip away. For years, he reappeared through video tapes or recordings, taunting the United States and issuing new threats, only to slip away again to the dismay and frustration of U.S. officials.

Bin Laden eluded Bush and his team, to their regret, but not for lack of trying. Bush’s persistence was palpable and set the tone for the intelligence community tasked with bringing bin Laden to justice. Obama picked up on that commitment when he came into office and redoubled efforts to defeat al-Qaeda and kill bin Laden.

Obama authorized an increase in the use of Predator drones to kill al-Qaeda leaders. Even before he was president, he made headlines — and drew attacks from some of his rivals — for announcing that, if he were president and had actionable intelligence, he would not hesitate to send U.S. forces across the border from Afghanistan into Pakistan to take out terrorists.

That is exactly what happened Sunday, according to the president’s statement. Obama said he earlier had directed Leon Panetta, the director of the Central Intelligence Agency, to make the pursuit of bin Laden the agency’s top mission. On Sunday, based on intelligence information, a small team carried out the mission that killed the terrorist leader inside Pakistan. Experts called it one of the greatest intelligence victories in the history of the country.

Among those who hailed the news was the former president, who was called by Obama before the public announcement. “This momentous achievement marks a victory for America, for people who seek peace around the world, and for all those who lost loved ones on September 11, 2001,” Bush said. “The fight against terror goes on, but tonight America has sent an unmistakable message: No matter how long it takes, justice will be done.”

The attacks on Sept. 11 united Americans as few contemporary events have done, producing a sense of goodwill across partisan lines and broad support for the war in Afghanistan, which was launched little more than a month after the attacks.

That unity and goodwill eventually eroded, especially as a second war against Iraq soured in the aftermath of an invasion that toppled Iraqi leader Saddam Hussein from power, and Bush’s presidency never recovered from the divisions that Iraq and other issues created.

Obama is in the midst of bringing that Iraqi conflict to a close, but he has sharply escalated the war in Afghanistan. Public opposition to that war has been growing, with more than six in 10 Americans now saying the war in Afghanistan has not been worth it. Obama faces a July deadline to begin drawing down U.S. forces there, as he has pledged, but he will have a difficult job of managing public support depending on how slow that drawdown becomes.

The president will almost certainly receive a boost politically from the killing of bin Laden, but it could also bring greater calls for him to bring the war there to a close even more rapidly.

But the death of bin Laden will probably bring the country together. To Americans, bin Laden became a hated man. The sense of relief and, even, triumph that accompanied the news underscored both how the attacks of Sept. 11 had scarred the nation’s psyche and how much the killing of bin Laden was seen as a measure of justice having been done.