Was there a real reason for the US to invade Iraq in 2003?

To me it seems that the US invasion wasn't justified and that the real reason was not to dispose of Saddam but for other reasons. Actually I heard that one reason was for access to oil, especially in the future, but after invading they didn't find any. It all leaded to the great migration wave of 2015 and more terrorism in the future. And naturally the US spent billions of dollars and many American Soldier's died.