Why iraq's people kill soldiers

U.S. and U.K. release iraq's people from suppression.
But iraq's people kill soldiers of U.S. and U.K.
Why?
 
Please teach...

My dad, who has actually been over in Iraq this last year, told me most of the people are glad to have us. The people who are still fighting are people who hate us and love Saddam. If Iraq becomes a democracy, they will lose their power. Therefore, they try to kill us.