Whats the reason for the war in iraq? ?

I started thinking about the war and i realized that i never understood it at all. Im fourteen now so i was about 4 or 5 when the 9/11 attacks happened. Can you tell me what the real reason for the war in iraq is about? I use to think it was about oil but yeah lol im pretty that is wrong... As of now i think america is wrong for invading other countries and destorying them but americans blame the other country that their soldiers are dying in the war. What about the thousands of innocent people in iraq dying just because they live there? Like their homes are being destroyed and americans can only think about their soldiers who could choose not to fight while the innocent citizens cant really go anywhere. So whats the reason for the war? and is it going to end soon?