Bush/Cheney/Rummy definitely are to blame for Iraq, and they just used the 9/11 as an excuse to go in there. We will never know the truth about the CIA reports of WMDs, but the 3 of them were more than willing to go in on limited facts as they really wanted to remove Saddam from power. Congress at the time was easily convinced that it was the right thing to do.
W wanted to be a war president and definitely got his wish.
Actually, China is involved, but they simply move in after the major fighting is done and start throwing money around, which the Iraqi government is more than happy to accept. They are low profile so they never come up as a target for the extremists, but they definitely have their foot in the door. They are in a lot of African countries doing the same thing.
Obama had no choice as the exit was an agreement Bush had signed with the Iraqi government years before. Republicans fail to mention that part when complaining about the exit and how it is a major failure of the Obama Whitehouse.
Obama tried to keep some forces in country, but the Iraqi government was having nothing to do with it. I am sure they regret that decision now.