What happened as a result of the us invasion of iraq in 2003?

Saddam Hussein was convicted of war crimes and executed.

The war in Iraq was pursued beginning in 2003 as a preemptive strike against the regime of Saddam Hussein and the perception that he had stockpiles of weapons of mass destruction that could be used for terroristic purposes.  That perception did not turn out to be a full reality, but the war pursued regime change in Iraq nonetheless.  Saddam Hussein was removed from power.  Later, in 2006, Hussein was convicted of crimes against humanity by the Iraqi Special Tribunal.  He was executed by hanging.