TEN YEARS WITHOUT AN ATTACK

John Yoo in WSJ on September 6, 2011, reminded readers that in the decade after 9/11 the most incredible thing to happen was this: nothing.

After 9/11, terrorism experts inside and outside the government all agreed that more attacks would come. The coordinated hijackings revealed our open society’s vulnerability and displayed the resources, sophistication and determination of a deadly enemy. Al Qaeda had a committed, intelligent leadership, a safe harbor in Afghanistan with dozens of training camps and thousands of trained fighters, and an ideology that appealed to frustrated, oppressed men in the Arab world. It had a track record of returning to the same targets; it had tried to blow up the World Trade Centers with a truck bomb in 1993.

No one would have predicted that George W. Bush, and his successor, Barack Obama, would succeed in preventing another successful and disastrous terrorist attack.

Looking back over the decade, the first clear lesson is the critical importance of Mr. Bush’s decision to consider the struggle with al Qaeda a war. Unlike past administrations, his chose not to view al Qaeda as a Middle Eastern version of the mafia, if on a grander scale. The 9/11 attacks constituted an act of war—they were a decapitation strike, an effort to eliminate our nation’s leadership in a single blow. If the Soviet Union had carried out the same attacks, no one would have doubted that the United States was at war.

Al Qaeda’s independence from any nation state would not shield it from the American military and leave it solely to the more tender mercies of the FBI and the courts.

Choosing war opened the arsenal that has decimated al Qaeda’s leadership and blunted its plan of attack. A nation at war need not wait for a suicide bombing to arrest the “suspects” who remain. Instead, it can fire missiles or send in covert teams to pre-emptively capture or kill the enemy. Our government doesn’t need a judge’s permission before tapping an al Qaeda operative’s phones, intercepting his emails, or arresting him.

We need not provide terrorists with Miranda warnings, lawyers and jury trials. A nation at war can detain the enemy without lawyers or civilian trials and interrogate them for information to prevent future attacks.

In its second critical decision, the Bush administration pushed to translate knowledge into action. Winning the war requires, above all, the gathering, analysis and exploitation of intelligence. Before 9/11 our national security bureaucracies, prodded by the civil liberties worries of the courts and Congress, had deliberately handicapped their ability to pull all intelligence into a single mosaic. Passage of the Patriot Act, the expanded interception of international terrorist emails and phone calls, and the tough interrogation of a few high-ranking al Qaeda leaders broadened and deepened the pool of information on our enemy.

At the same time, the intelligence community and the U.S. Armed Forces have honed the integration of tactical intelligence and operations to a deadly knife’s-edge. Bin Laden’s killing this summer was not a one-off lucky shot, but the culmination of a decade of work combining intelligence-gathering, analysis and rapid strike teams. American presidents did not have such reliable options in the past—witness Jimmy Carter’s disastrous attempt to rescue the Iranian hostages or Bill Clinton’s failure to kill or capture bin Laden.

Americans were justifiably proud of the soldiers who carried out the difficult bin Laden operation. But what should impress them even more is that our special forces are carrying out similar missions every night of the week.

Improved intelligence and more lethal special forces allowed the United States to disrupt plots at home. This included plans to blow up office and apartment buildings as well as airliners flying across the Pacific and Atlantic. We have killed or captured most of al Qaeda’s first and most capable leaders.

The third lesson of the last decade is that, despite this war mobilization, domestic individual rights proved far more robust than critics claimed. Reacting furiously to the war paradigm, members of the academic, political and media elite predicted the end of liberty in our time. They saw in Guantanamo Bay, interrogations, military courts and electronic surveillance the emergence of a new national security state that would transform American society for the worse.

But individual freedom emerged from the decade stronger than before. The government did not censor the media, sabotage political opposition or mobilize the economy. No dictatorship arose. As the Constitution intends, the executive, legislative and judicial branches freely used all of their powers to struggle for influence over national security policy. Five bitterly contested national elections (the true check on any abuse of power) switched control of the presidency once, the Senate once, and the House of Representatives twice. Meanwhile, new technologies and social networking have created an expanding space for political activity and organization unlike anything in our history.

Civil liberties would certainly have suffered far worse had al Qaeda succeeded in landing a second blow on a par with 9/11. Instead, the Bush administration successfully handed off a secure homeland to its successor. Mr. Obama fumbled with his failed effort to close Gitmo, try al Qaeda leaders in Manhattan, and prosecute CIA officers. Yet reality and political opposition forced the administration to return to many of its predecessor’s core terrorism policies.

In the last decade, our nation has certainly paid a price in the lives of the brave men and women who have defended us. But who would say, after 10 years, that it wasn’t worth it to keep our nation safe?

Mr. Yoo is a law professor at the University of California, Berkeley. He was an official in the Justice Department from 2001-03, and is co-editor of “Confronting Terror: 9/11 and the Future of American National Security,” just published by Encounter Books.