Who says the war was over when Saddam was removed?
BTW, do you actually know history. Did you know that after WWII there was lots of fighting for years with factions who refused to give in, both in the pacific as well as germany, etc...
The USA and allies who stayed to help rebuild those areas and defend them after the war was over were being shot at just the same. This is true of Iraq as well. The war has been over it is now not really a war but a rebuilding effort with a huge faction of extremists who refuse to allow the fighting to be over.
You would do well to read a history book.