After 13 years of war, President Barack Obama this week declared the end of U.S. combat operations in Afghanistan. "Our combat mission in Afghanistan is ending, and the longest war in American history is coming to a responsible conclusion,'" Obama said in a statement from Honolulu, where he is spending his Christmas vacation.

But that should not be taken to mean that there will be no U.S. forces in the country, nor that they will not be engaged in warfare in the new year.  Here are five reasons why.

Afghanistan wants help

American troops will remain in Afghanistan for at least two more years. A day after his Sept. 29 inauguration, Afghan President Mohammed Ashraf Ghani signed a bilateral security agreement with the U.S., extending the American military presence in his country beyond this year. Obama has announced plans for a phased withdrawal of troops over the next two years that will leave about 5,500 there by the end of 2015 and 1,000 by the beginning of 2017, when he leaves office.