Washington (CNN) -- President Barack Obama announced Wednesday night that all the 33,000 additional U.S forces he ordered to Afghanistan in December 2009 will be home within 15 months.

In a nationally televised address from the East Room of the White House, Obama said 10,000 of the "surge" forces would withdraw by the end of this year, and the other 23,000 would leave Afghanistan by September 2012.

Calling the deployment of the surge "one of the most difficult decisions that I've made as president," Obama said the military campaign was "meeting our goals" in Afghanistan and the drawdown would begin "from a position of strength."

"Al Qaeda is under more pressure than at any time since 9/11," Obama said. "Together with the Pakistanis, we have taken out more than half of al Qaeda's leadership. And thanks to our intelligence professionals and special forces, we killed Osama bin Laden, the only leader that al Qaeda had ever known. This was a victory for all who have served since 9/11."

At the same time, Obama said the Afghanistan drawdown and the simultaneous winding down of the war in Iraq would help the United States begin to refocus attention and resources on efforts to resolve economic and other problems and to unify a politically divided nation.

"America, it is time to focus on nation building here at home," the president said.

The troop withdrawals from Afghanistan will begin next month, as Obama promised when he ordered the surge in a speech 18 months ago at the U.S Military Academy at West Point, New York.  U.S. Defense Secretary Gates Visits Afghanistan

After the departure of all the surge forces, the total U.S military deployment in Afghanistan will be slightly fewer than 70,000 troops.

Obama's time frame will give U.S commanders another two "fighting" seasons with the bulk of U.S forces still available for combat operations.