President Obama's plan to keep 9,800 U.S. troops in Afghanistan after the end of the combat mission this year will begin the full withdrawal of all U.S. military forces from Afghanistan by the end of 2016, bringing an end to America's longest war.

Over the course of the almost 13 years of the conflict, 831,576 service members have served at least one tour of duty in Afghanistan. Some 2,184 American service members have lost their lives and 19,600 have been wounded in a war that has cost $537.8 billion.

There are currently 32,800 American service members serving in Afghanistan. If a bilateral security agreement is signed by Afghan President Hamid Karzai's successor, the plan unveiled today by President Obama calls for a reduction of the U.S. force to 9,800 trainers and counterterrorism forces by the end of this year.

(Noorullah Shirzada/AFP/Getty Images)

That number will be halved to 4,900 by the end of 2015 and by the end of 2016 the U.S. military footprint will be reduced to a presence at the U.S. embassy in Kabul.

That's almost where U.S. military troop numbers stood at the very start of the war before eventually growing to 100,000 a decade later.

In the immediate aftermath of the 9/11 attacks the Pentagon planned for a limited military engagement to eliminate the safe haven provided to al Qaeda by Afghanistan's Taliban government. U.S. military planners developed a plan to conduct that mission with a very small footprint of American troops that relied on Special Operations forces quietly working with the Taliban's enemies inside Afghanistan.

That mission began on October 7, 2001 when American cruise missiles and bombs rained on al Qaeda training camps in Afghanistan. By then small groups of Special Operations teams had snuck into Afghanistan to work with Northern Alliance fighters fighting Taliban forces. The first large-scale U.S. military operation came in late October when Army Rangers parachuted into Kandahar Province to establish the first U.S. military base in Afghanistan, Camp Rhino.

By November, 2001 there were 1,300 troops in Afghanistan, a month later those numbers would double to 2,500. The footprint of U.S. forces would remain small for years, not rising above 10,000 until 2003 and not reaching 20,000 until 2006.

By then a resurgent Taliban brought requests from military commanders for additional forces. By late 2008 the Bush administration met some of those requests so that by the time that President Obama entered office in January, 2009 there were 34,400 U.S. military forces in Afghanistan.

But military commanders requested even more forces of the new Obama administration which had campaigned on a platform to end the war in Iraq and re-focus the military fight in Afghanistan.

By March, 2009 President Obama had ordered 21,000 additional forces to Afghanistan. Six months later months later he ordered an additional 33,000 surge forces to meet a request by Gen. Stanley McChrystal for more troops to focus on a counterinsurgency mission.

U.S. troop levels in Afghanistan eventually peaked at 100,000 in August 2010 and from March to May of 2011. Nearly ten times the number of forces there almost a decade before.

But President Obama had placed a timetable for the presence of the elevated surge numbers setting July, 2011 as the beginning of the draw-down of those forces. By the end of 2012 American troop levels had returned to pre-surge levels of 68,000.

In his State of the Union address in February, 2013 President Obama announced that in a year's time the size of the U.S. force would be reduced by half.

That's where force levels have remained while the administration has waited for Hamid Karzai's successor to be elected after his refusal to sign the bilateral security agreement that would ensure the presence of American troops after 2014.