President Obama made an unannounced trip to Afghanistan Tuesday, arriving under the cover of darkness to sign the agreement.
At the presidential palace in Kabul, Mr. Obama talked about the importance of the document, which sets out a 10-year strategic partnership after NATO forces end their combat role in 2014.
“Together, we are now committed to replacing war with peace, and pursuing a more hopeful future as equal partners," said President Obama.
After expressing thanks to U.S. troops at Bagram Air Base, Mr. Obama announced the agreement to the American people.
“Today, I signed an historic agreement between the United States and Afghanistan that defines a new kind of relationship between our countries," said Obama.
The president said that at this month’s NATO summit in Chicago, the coalition will set a goal for Afghan forces to be in the lead for combat operations across the country next year.
“International troops will continue to train, advise and assist the Afghans, and fight alongside them when needed," he said. "But we will shift into a support role as Afghans step forward.”
The agreement signals that the U.S. will continue to work with Afghanistan in the long term, according to Brian Katulis, a senior fellow at Washington’s Center for American Progress.
“This agreement will offer that reassurance that we are not going to abandon them, that we will actually be with them, and that we will work with them," said Katulis.
Katulis says the strategic agreement also gives the Afghan government incentive to tackle its longstanding problem with corruption.
“For the Afghan people, I think this agreement will tangibly send this message that the United States and its NATO allies will continue to provide economic support, will help you diplomatically - if you fulfill your commitments," he said.
The agreement was signed exactly one year after U.S. Navy SEALs killed al-Qaida leader Osama bin Laden in Pakistan.
And the president reminded Americans that the original goal of the war - disrupting al-Qaida’s ability to launch terror strikes - had been met.
“This time of war began in Afghanistan, and this is where it will end," said Obama.
Mr. Obama reassured Mr. Karzai that the U.S. has accomplished its aim in Afghanistan, and will not build permanent bases there.
The U.S. has more than 90,000 troops in Afghanistan. That number is expected to shrink to 65,000 by the end of this year, and to fewer than 20,000 by the end of 2014.