President Barack Obama opened the NATO summit by saying the alliance is bringing stability and peace to Afghanistan but added there will be "hard days ahead."
"I look forward to our meeting with our NATO neighbors and partners around the world that have been so critical to NATO operations as in Afghanistan and Libya
President Obama met with Afghanistan's President Hamid Karzi privately Sunday morning.
Karzai said the transition in his country will mean that Afghanistan is "no longer a burden" on the rest of the world.
Standing next to Obama, Karzai thanked Americans for the help that their "taxpayer money" has done in Afghanistan.
The allies are expected to reach agreement on details to transition international troops out of Afghanistan that would leave support for the people of Afghanistan.
"We will not walk away," said NATO Secretary General Anders Fogh Rasmussen. "Once transition is completed, NATO will lead a new mission to train, advise, and support the Afghan security forces."
President Obama welcomed the world leaders back to visit Chicago once the Summit has concluded.
Mayor Emanuel made an unexpected visit to the media center of the summit. He expects the summit will lead to future visits
"The world leaders... they are blown away by the beauty, the kindness of the people," Chicago Mayor Rahm Emanuel said. "And so this is a great opportunity for the city, for the world to come see our city and for the city to see the world." The Associated Press contributed to this report