Peace activists demonstrate at the Times Square in New York, the United States, on March 20, 2010, to mark the 7th anniversary of the war on Iraq.  [Photo: Xinhua]

On the seventh anniversary of the U.S. invasion of Iraq, the United States can point to many lessons from the conflict.

But some lessons are not new. Rather, they are forgotten lessons that had to be re-learned. And the question remains whether Washington is doomed to re-learn them yet again, experts said.

At the start of the war in 2003, the "shock and awe"campaign quickly overwhelmed Iraq's armies and U.S. forces claimed victory in a matter of weeks. But as the Bush administration celebrated, attacks on U.S. forces began to occur. And after a period of denial, the administration was forced to concede that it had an insurgency on its hands.

But while the United States had engaged in a number of counter insurgency operations throughout its history, the Pentagon had forgotten how to fight an unconventional enemy.

Nate Hughes, military analyst at Stratfor, a global intelligence company, said the United States had forgotten much of the counter insurgency knowledge it gained in Vietnam.

After that conflict, the Pentagon shelved its counter insurgency manuals and busied itself planning for a "conventional war"- an army-to-army conflict on an open battlefield, as opposed to a "guerrilla war"-as Washington never thought the United States would fight another Vietnam, he said.

"It's not that we wrote our first counter insurgency manual in the last decade," he said. "We just stopped publishing one."

Indeed the United States has fought insurgencies everywhere from the Philippines to Haiti - two long forgotten conflicts of the early 20th century. But some experts say the United States is doomed to repeat the mistakes it made in prior wars, including Iraq.

"As soon as Iraq and Afghanistan are over, and the resources are strained, are we going to retain all the knowledge we have gained or are we going to throw it aside like we've done every other time in the past?" said James Carafano, defense expert at the Heritage Foundation.

Experts said one major mistake in Iraq was a lack of a clear exit strategy, a blunder also made in Vietnam. Partly from that experience came the Powell Doctrine, named after General Colin Powell, secretary of state under the Bush administration.

But the doctrine, which calls for a clearly defined objective, the use of overwhelming force and strong international support for U.S. military operations, got lost once U.S. forces found themselves embroiled in a seven-year guerrilla war in Iraq.

Michael O'Hanlon, defense policy expert at the Brookings Institution, said some lessons learned in Iraq were old ones that had been forgotten, including the core principals of counter insurgence.

But the use of new tools such as surveillance drones, the specific methods for helping reform the Iraqi police and army, and means of countering suicide bombs and roadside bombs -one of insurgentsmost deadly tools-were in some cases new.

One major lesson was that a military force cannot fight its way out of an insurgency. Rather, proper counterinsurgency requires protecting the local population, developing intelligence networks by cooperating with locals and building up state institutions, he said.

In future wars, it is possible for the United States to forget the knowledge gained in Iraq, given the complexities involved and the opportunity costs when other military missions demand attention as well, he said.

Still, the United States will likely emerge from this period being more successful in counter insurgency than in Vietnam. Washington will also recognize that counter insurgence is even more central to U.S. national security today than it was in the 1970s, he said.

As such, the United States stands a good chance of remembering Iraq's most crucial lessons, and military planners are still focused on counter insurgency in Afghanistan, he said.

Christopher Preble, director of foreign policy studies at the Cato Institute, said that usually wars are so unique that few lessons carry over from one conflict to the next. So whatever the United States learned in Iraq may or may not be able to be applied to the next war, he said.

Rusty Barber, director of Iraq programs at the U.S. Institute of Peace (USIP), said it remains unclear whether civilian organizations engaged in post conflict operations in Afghanistan are heeding the lessons of Iraq.

One problem in Iraq was a lack of coordination between non-governmental organizations and the military, an issue that could emerge in Afghanistan, said Barber, who led the USIP stabilization projects in Iraq.

Critics have also said Washington assumption that Iraqis would welcome U.S. troops as liberators was naive at best and destructive at worst.

"We have this messianic need to spread democracy," he said, "and have it bloom overnight. In other words, if we plant that seed-even if we have to use force to do it-it will take root. That isn't always the case."