The decision to invade Iraq in 2003 was a big mistake. The purpose of the invasion was to find weapons of mass destruction that supposedly Saddam Hussein was in possession of. However, no such weapons were found. Bush Jr. also invaded Iraq to finish the job that he believed his father should have done. If Bush Sr. decided not to dethrone Saddam, what makes Jr. justified? The effects of the invasion don't justify exposing the entire country to the horror and desolation of war: countless Iraqi civilians killed and displaced, the Iraqi military disbanded.
Saddam Hussein was a terrorist. If we would have let him continue to run his country, millions of people would have died. We aided civilians in the middle east who were in dire need of help. We tried hundreds, even thousands of terrorists who have killed thousands of people.