As the current crisis in Iraq unfolds, some Iraq war veterans are asking if all the gains made by U.S. forces have been lost.
When former Army Capt. Blake Hall left Iraq in 2007, he remembers being hopeful.
"Iraq had an opportunity for long-term political reconciliation," Hall told CBS News correspondent Jan Crawford.
Two years later, Army Sgt. Matt Pelak had a similar feeling when his service was over. He saw progress among the Iraqi army and people his unit trained.
"You'd see more Iraqi army and Iraqi police on the streets, and you got the feeling that, yeah, maybe they're getting their act together," Pelak said.
However, they were also were realistic -- and fearful -- about the challenges ahead.
"Since I've left the country, it's been slowly slipping towards this exact moment. But you could see it coming," Hall said.
As the situation in Iraq deteriorates, many veterans like Hall and Pelak are questioning what their service accomplished.
Hall said he thinks it was a mistake not only to go into Iraq, but also to leave it.
"You break it, you buy it, right? Once you go in-- I think America has a moral responsibility," Hall said. "I lost my friends. I want their deaths to mean something. I want my service over there to mean something."
In the nine-year war, 4,400 American troops died in Iraq. More than 32,000 were wounded, and the U.S. spent more than a trillion dollars.
"It's hard to justify that when you can't put a clear definition of success and have a road map on that," Pelak said. "It's pretty frustrating from a soldier's perspective."
When he campaigned for president in 2008, then-Sen. Obama made bringing the troops home a priority.
The last American service members left Iraq in December 2011, but the U.S. withdrawal came at a cost, leaving an opening for radical terror groups.
"If you start to make decisions without understanding the long-term consequences, you put the United States of America in a worse position," Hall said. "And that's frustrating for all of us who've fought in these wars."
Hall said it is difficult to put into words.
"It's a blend of anger and it's a blend of love for my guys and for what they did. And it's sadness for all of my friends who I've lost. But there is no word that captures the emotion of having seen Americans sacrifice the way that they've sacrificed, and yet, nothing come of it."