We know that Iraq was not involved in sep 9/11 ,US was not to rob oil then why invade Iraq & kill so many ?

Surely the US and the willing do not care about dictatorship or the people of Iraq .Many people in other countries suffer worst than what Iraqi people did for example Iran ,Korea, Burma ,USSR(in the past) just to mention a few .I am confused as do not understand the reaason for the invasion or the benifit from it for the US or the willing .All I can see death and destruction on all sides .