What? There's a War?

AP story:

"WASHINGTON - Fueled by fierce fighting in Fallujah and insurgents' counterattacks elsewhere in Iraq (news - web sites), the U.S. military death toll for November is approaching the highest for any month of the war."

There's a war in Iraq? A war? Didn't the US win that war like a year-and-a-half ago? Then how could it still be going on?

Explanations sought.