U.S. President Barack Obama on Tuesday announced the end of combat operations in Iraq, saying the United States has met its responsibility, and "it is time to turn the page."

"Tonight, I am announcing that the American combat mission in Iraq has ended. Operation Iraqi Freedom is over, and the Iraqi people now have lead responsibility for the security of their country," Obama said in an Oval Office address to the nation.

According to agreements between the two governments, U.S. troops are due to end combat mission in Iraq on Aug. 31, and will transition into a mission to mainly advise and assist Iraqi security forces. The Pentagon said the remaining 50,000 U.S. troops will also support Iraqi troops in targeted counter-terrorism missions, and protect U.S. civilians.

While announcing the U.S. combat mission is ending, Obama said the U.S."commitment to Iraq's future is not," as U.S. diplomats, aid workers, and advisors are "moving into the lead to support Iraq as it strengthens its government, resolves political disputes, resettles those displaced by war, and builds ties with the region and the world."

The president's speech came at a time when Iraq's future seems very much in doubt.

Besides lacking a fully capable national army, Iraqis was unable to form a government months after the March 7 parliamentary elections.Militants exploited the political vacuum, mounting deadly attacks all over the country.

Even a stable, friendly Iraq "will take a minimum of another five years, and probably ten" of intense nation building efforts, said Anthony Cordesman, a defense and security expert with the Center for Strategic and International Studies.

No wonder Obama used the speech to renew his call for Iraqi leaders to form an inclusive government "with a sense of urgency."

Reflecting on the huge costs of the war, Obama said ending it is not only in Iraq's interest, it is also in the Unites State's own.

"We have sent our young men and women to make enormous sacrifices in Iraq, and spent vast resources abroad at a time of tight budgets at home."

United States has spent over 7,000 billion U.S. dollars in the war, with more than 4,400 troops killed and more than 30,000 others wounded. Overall costs of the war could amount to three trillion dollars if medical expenses for injured veterans are counted.

The United States is also fighting another war in Afghanistan. Obama said because of the drawdown in Iraq, the administration "is now able to apply the resources necessary to go on offense." He has ordered additional deployment of 30,000 troops to Afghanistan late last year.

Obama has set next July as the beginning of the troop drawdown in Afghanistan, though "the pace of our troop reductions will be determined by conditions on the ground."

"Make no mistake: this transition will begin," Obama said, noting open-ended war serves neither U.S. nor Afghan interests.

As the country begin to wind down the Iraq war and setting sight on an end to the Afghanistan war, Obama said U.S. influence around the world should not be a function of military force alone, but also a projection of the country's diplomacy and economic strength.

Burdened by two unpopular wars, the U.S. economy is slow to recover from a deep recession.

"We have spent over a trillion dollars at war...This, in turn, has short-changed investments in our own people, and contributed to record deficits," Obama said, vowing to restore the economy, and "put the millions of Americans who have lost their jobs back to work," Obama said.

"In the days to come," reviving the economy "must be our central mission as a people, and my central responsibility as president," Obama said.

He promised to strengthen the middle class, improve education, jumpstart industries, end dependence on foreign oil, as well as unleash innovation.

This is the second Oval Office speech Obama made as president. He used his last one to address the BP oil spill. This time, he steered clear of a "victory lap," and called former president George W. Bush, who started the Iraq war, before the speech.