WASHINGTON -- Gen. John Abizaid used the phrase "the long war" to describe America's battle with Islamic extremism after Sept. 11, 2001. When I first heard him say it in the dark days of 2004, as Iraq was spiraling downward, I had the feeling that it would last for most of our lifetimes.

Behind this decades-long battle, Abizaid said, was the political modernization of the Islamic world -- the explosive process of change that he likened to the revolutions and anarchic movements that swept across Europe in the 19th century.

This is the overarching conflict from which Barack Obama wants to withdraw American troops -- not because the turbulence is over but because big American expeditionary forces aren't the right answer. He suggested this larger shift Wednesday night. After a "difficult decade," he said, "the tide of war is receding. ... These long wars will come to a responsible end."

You can fault some of the particulars of Obama's policy. I'm scratching my head about the logic of his timetable for reversing the surge he announced 18 months ago: Pulling out 10,000 troops this year is OK, but why yank out another 23,000 in the middle of next year's fighting season? That encourages a battered Taliban to hang on awhile longer, rather than bargain for a truce. It repeats the tip-your-hand mistake I thought Obama made back in December 2009, when he set a date for beginning the withdrawal of his surge forces even as he ordered them into battle.

But on the larger theme, I thought Obama had it right. This period of expeditionary wars does need to come to an end -- not just because America is weary and broke, but because the dialectic of history has brought the world to a new place. If American military might has been shown to have limited effect in shaping events over the past 10 years, so have the terrorist strategies of al-Qaeda and the Taliban.

When Osama bin Laden declared war on the United States in the 1990s, he made two assumptions, both of which turned out to be wrong. He argued that if America were hit hard by a terrorist attack, it would run away, just as it had from Lebanon after the 1983 bombings and from Somalia in 1994. In his last moments, bin Laden surely knew this bet on American softness had been mistaken. "The message," said Obama, quoting an unnamed American soldier, "is we don't forget. You will be held accountable, no matter how long it takes."