Anybody know the reason why the US of A invaded Iraq?

I really would like to know why the US went into Iraq. At first I heard it was because of WMD's. When no WMD's were found, they said it was because Saddam was committing genocide against the Kurds. Also, his sons were raping and murdering innocent people. And Saddam was paying the families of suicide bombers every time they struck in Israel. Then Bush says "He tried to kill my dad." And I also heard Saddam wanted to sell his oil for Euros instead of US dollars. I know there were more excuses which I can't recall now. So--- I will ask, why is the US in Iraq?