If one theme sums up President Obama’s first extended foreign trip, it is this: The era defined by 9/11 is over. It’s time to turn the page and start a new historical cycle marked by different issues and changing relationships.

In London, at the beginning of his trip, Obama advanced his theme by emphasizing that the “gravest threat” to American security was not unbridled Islamic terrorism but uncontrolled nuclear weapons. In reopening arms-reduction talks with Russia, he was saying, in effect, that Vladimir Putin remains more important to the national interest than Osama bin Laden.

But the most intriguing moment was a town-hall meeting he held with students in Istanbul at the end of his eight-day journey. “I came to Turkey,” he told them, “because I am deeply committed to rebuilding a relationship between the United States and the people of the Muslim world – one that’s grounded in mutual interest and mutual respect.”

That tone contrasts sharply with his predecessor. George Bush presided over a country deeply traumatized by the horrific events of September 2001. He launched a “crusade” (a word he later jettisoned) against a Muslim country, captured and jailed hundreds of Muslims, and vowed to seize the leaders of Al Qaeda “dead or alive.”