The U.S.-led invasion of Iraq started in the Spring of 2003.  As of this writing some 13,000 American fighters are in the country, down from a one-time high of 170,000.  The deadline for all of those troops to withdraw from Iraq is a little more than a month away, on December 31st.  Convoys of soldiers have already started to ship out.  But as Michael Holmes explains, the pullout has been a long and complicated process.