Explain the background of the war of Iraq.

To understand the Iraq War, you must understand a number
of basic facts about the history of the region.

First, you
must understand that the US (and a coalition of allies) went to war against Iraq in
1991.  This happened because Iraq had invaded and occupied neighboring Kuwait.  The
US-led forces went to war to force Iraq out of Kuwait but did not try to overthrow the
Iraqi government after they had liberated Kuwait.

Second,
you must understand that Saddam Hussein, the dictator of Iraq in those times, worked on
a program of trying to obtain weapons of mass destruction, also known as WMD, such as
biological and chemical weapons.  He refused to allow UN inspectors free access to make
sure that he was not actually trying to get WMD and that he had destroyed ones that he
already had.  The US felt sure that, in 2003, he still had WMD that he would not admit
to having.

Finally, you must understand that many in the
Bush Administration felt that Iraq was in some way tied to the 9/11 terror attacks. 
They felt that leaving Hussein in power in Iraq would leave the US vulnerable to further
attacks.

It was largely for these three reasons that the US
invaded Iraq in 2003.  The US felt that Hussein was a "loose cannon" who had WMD and
might use them to destabilize the region or even to attack
America.