Army Chief of Staff Gen. Raymond Odierno believes that if U.S. troops had been allowed to remain in Iraq past 2011, the likely could have prevented the rise of the Islamic State by encouraging disparate political factions within the Iraqi security forces to work together.

He took charge as chief of staff in 2011, the same year U.S. troops left Iraq seemingly for good. He will leave that office and his 38-year Army career on Aug. 14 with just over 3,000 U.S. soldiers again in Iraq, helping that nation’s beleaguered security forces route Islamic State (ISIL) militants. Odierno said ISIL was able to exploit the political vacuum that took hold after U.S. forces left to carve out a huge swathe of Iraq and Syria and establish their brand of extremism.

“As I look at Iraq…it is frustrating,” he said Aug. 12 during a farewell press conference at the Pentagon. “I believe that a couple years ago, 2010-2011, we had it in a place that was heading in the right direction. Violence was down, the economy was growing. The politics were OK.”

Then the U.S. military in 2011 turned the country over to the Iraqis, as agreed to under the status of forces agreement negotiated in 2008 under then-President Bush.

“As it has turned out, they weren’t prepared to handle that,” he said. “The political factions just simply weren’t able to work together and based on that, people became frustrated. When people become frustrated, they tend to turn to violence when there is no other way for them to make their point. That allowed a group like ISIL to exploit the fissures that were occurring inside Iraq.”

Odierno said he has learned that there are limits to military power and what can be accomplished by military action alone. As with ISIS, a sizable U.S. military force could likely invade and destroy all of their fighters with relative ease, but “do we achieve a sustainable outcome?”

In Iraq “the problem we have had is we have had outcomes, but they have been short term… because we haven’t properly looked at the political and economics sides of this,” he said. “There has got to be all three coming together. If you don’t do that, it’s not going to solve the problem. I absolutely believe that the region has to solve this problem.”

“The U.S. cannot solve this problem. They have got to get involved and be part of the solution… We could probably go in there with a certain number of American forces and we could defeat ISIL. The problem is we’d be right back today where we are six months later.”

Odierno described the fight against ISIL in Iraq and Syria as at a “stalemate” while U.S. advisers continue to train Iraqi troops and other local forces, including Syrian rebel forces, in preparation for a major offensive against the terrorist group.

If in the next several months the current U.S. plan to degrade and destroy ISIL through a combination of training local troops and conducting airstrikes has stagnated, “we should absolutely consider embedding some soldiers and see if that would make a difference.”

Placing troops in forward deployed Iraqi units to serve as tactical air controllers, not as combat troops, then “should be an option we present to the president when the time is right,” he said.

If ISIL were a direct threat to the United States and were discovered plotting an imminent attack on U.S. soil, then military leadership should consider advising the president to deploy large numbers of troops, he said. That is not currently the case, he added.

“We have to stop a group that is attempting to be a longterm influence in the Middle East that is promoting extremism and, frankly, suppressing the populations in the Middle East,” he said. “In order to resolve that, we need the countries in the Middle East and surrounding the Middle East to be involved with the solution.”

The U.S. military was legally obligated to leave Iraq in 2011, which extended a U.N. mandate that set the exit deadline in 2008. After that point, U.S. troops were in Iraq with permission of the Iraqi government. Knowing how the situation would deteriorate, Odierno said he may have tried harder to negotiate another extension with the Iraqis, but he was not commander at the time and would not comment further.

“What I would say is, having military on the ground allowed us to be honest brokers between some of these groups and I think, maybe, as we all look back, leaving some soldiers on the ground might have helped a little bit and may have prevented where we are now,” he said.

Odierno would not touch the question of whether the 2003 invasion was a mistake in the first place. He did say that the aftermath of the U.S. exodus from Iraq should inform the future of its military commitment in Afghanistan.

The enduring presence of the U.S. military was able to ensure that stable governments and social institutions were established in Germany and Japan after World War II, he said. Careful not to equate Germany and Japan with Iraq and Afghanistan, he said “having us there helps to establish an institution that is capable of being sustainable and lasting for a lot longer time.”