Frankly, I'm already appalled at some of the answers you've been getting, although I'm sorry to say I'm not surprised. Even now, more than 6 years after this whole thing started, people STILL don't know what the hell is going on in Iraq and many refuse to learn.
Number 1: We are not, repeat NOT, "at war with Iraq". We ceased to be "at war with Iraq" in 2003, shortly after the actual war started. After the war itself ended, our operations in Iraq ceased to be conventional warfare (since we easily defeated Saddam's military), and became counter-terrorism and counter-insurgency operations... what the military calls "Stability and Support Operations" or "Military Operations Other Than Warfare". (These are literally what the military calls it, by the way). Iraq is an ally, and has been since 2003, when we removed Saddam Hussein from power and helped set up a provisional government council, which eventually became the parliamentary democracy it is today, elected by Iraqis.
Point #2: Contrary to popular belief, this war was NEVER about oil. Next time you hear someone say that it was, stop them and ask them EXACTLY how much oil we are getting from Iraq. Seriously--ask them how much. Guess what? Iraq isn't really producing that much oil because their infrastructure isn't equipped to produce or refine more than a trickle of oil compared to their neighbors (Iran, Kuwait, Saudi Arabia, Syria...) What little they do produce generally goes elsewhere to be refined, and the people who use it are much more local... Iraqis themselves, and the neighboring Middle Eastern countries. Hell, the same people who think we're getting "all of Iraq's oil" also think we get most of our oil from Saudi Arabia, too. Well, we don't. Most of the oil we use in the United States comes from THIS hemisphere; oil from the US itself, then Canada and Mexico, then South America. Most of the oil the Middle East produces as a whole goes to more "local" customers... Europe, Russia, India, China, and the rest of Asia as a whole. As far as the money made from the oil Iraq DOES produce... that goes to Iraq and its government, because it's THEIR oil.
Point #3: We originally justified going to war with Iraq in the beginning (early 2003) because it was commonly believed that Iraq was pursuing weapons of mass destruction, even nuclear weapons. It wasn't just President Bush who believed that, either, even if people insist he made that decision unilaterally. Most of Congress believed it, too, as did dozens (yes, dozens) of other countries. Why? Because Saddam had a well-known history of pursuing nuclear weapons and developing them himself, and a history of not complying with international law and not allowing UN weapons inspectors to inspect where he was storing and developing his weapons. He also had a well-known history of starting wars with his neighbors and invading them (Iran in the 80's, Kuwait in the 90's). He was well-known for killing thousands of his own people, for silencing any whom he thought might be a threat to him by killing them and their families. As it turned out, he had also been laundering millions of dollars from the UN's Oil-for-Food program, money meant for his people... and a more than a few other countries knew about it, mostly countries who refused to help overthrow him because they profited off him. While we DID find some weapons of mass destruction (mostly to the tune of artillery shells laced with nerve agents or noxious gas), we did not find WMD to the extent we thought we would... but after we removed Saddam from power and he was in Iraqi custody, the conflict there ceased to be about "WMD" or overthrowing Saddam. We had removed Iraq's government, and it fell on us to help rebuild it and prevent Iraq from falling to the same fate as the South Vietnamese in the 1970's, or worse. Surprising as it may seem, it actually takes more than a few months to completely rebuild an entire country and its economy and military and infrastructure--all while also having to fight off gangs of insurgents and terrorists trying to kill you and Iraqis indiscriminately. The fact that we've come THIS far after only a mere six years is really, really remarkable.
Point #4: We're still here because the job's not yet finished. It's getting there, yes, and things are much better than they were even a year or two ago; but there are still many attacks taking place throughout Iraq and its people are still in danger from thugs and killers who want to subjugate them with fear and death in order to create a lawless haven for themselves. The military knows what it's doing. We've been at this for years now, and frankly the American people would do well to bother listening to what people who've actually BEEN to Iraq have been trying to tell them all these years. With any luck, we'll have the Iraqi government and its military able to fend for itself from internal, and external, threats by the time we do finally leave.
Point #5: This one seems to be a really tough one for people to grasp, and I really don't know why. The whole "War on Terror" was never JUST about 9/11, or JUST about "getting Bin Laden". The U.S. had been under attack by international terrorists before; 9/11 was just their "crown jewel". Al Qaeda is only one of many international terrorist organizations, and Bin Laden only one of many people in that organization. The War on Terror was meant to finally address a problem that the world had largely ignored, in the hopes that it would somehow "go away" magically by itself, for decades. "Weapons of Mass Destruction" wasn't even the only justification for invading Iraq in the first place, even though it was a main reason. Saddam Hussein and his government were state sponsors of terror, as the Taliban in Afghanistan had been. No, not sponsors of Al Qaeda... sponsors of Hezbollah in Israel and Lebanon. He helped financially and politically support a terrorist organization that has been around a lot longer than Al Qaeda, not to mention the fact that he'd been terrorizing, killing, maiming, gassing, and intimidating his own people directly ever since he took over Iraq in 1979. Our beef with Saddam had NEVER been because of the 9/11 attacks.