The junior Democratic senator from Illinois stood at the Victory Column in Tiergarten Park, buoyed by chants of "Obama, Obama, Obama" and applause for his call to defeat the ills plaguing the world.

"People of Berlin, people of the world, this is our moment," Obama said. "I know my country has not perfected itself. At times we've struggled to keep the promise of liberty and equality for all of our people. We've made our share of mistakes. And there are times when our actions around the world have not lived up to our best intentions. …

"The road ahead will be long. But I come before you to say that we are heirs to a struggle for freedom. We are a people of improbable hope. With an eye toward the future, with resolve in our heart, let us remember this history, and answer our destiny, and remake the world once again."

Obama recalled the fall of the Berlin Wall and the early days of the Cold War, just steps from the sites were former U.S. Presidents Ronald Reagan and John F. Kennedy delivered memorable anti-communist speeches. He used the backdrop for another call to arms.

"This is the moment when we must defeat terror and dry up the well of extremism that supports it. This threat is real and we cannot shrink from our responsibility to combat it," Obama said.