Obama says the costs of the Afghan war have been great. He says the deal with Afghanistan allows the U.S. to wind down the war, but still stand by Afghanistan and its people.
The president says the deal will also pave the way for "a future of peace."
Karzai says postwar agreement will seal an "equal partnership" between Afghanistan and the United States.
Obama and Karzai signed the agreement at the presidential palace in Kabul shortly after the U.S. president arrived in Afghanistan on Tuesday, slipping into the country under the cover of darkness.