As they meet again in Chicago, their main goal is to figure out how to make that happen.
The discussion among the alliance's 28 members takes place against the backdrop of shrinking defense budgets and economic hardship in much of Europe, and hard questions over NATO's future role in an increasingly complex global security landscape.
NATO Secretary-General Anders Fogh Rasmussen said last week that he fully expected NATO to continue training, advising, and assisting Afghan security forces, and saw the postconflict operation as "a new mission with a new role."
That new mission is expected to cost $4 billion annually, and Rasmussen expects leaders at the summit to firm up their financial commitments.
"In Chicago, we will also start to spell out our commitment to help finance the Afghan security forces of the future as part of an international community effort and together with the Afghans themselves," Rasmussen said. "We all have a stake in maintaining the gains we have made together with such great investment and sacrifices."
Stampede For The Door?
Most allies are planning a gradual withdrawal of combat forces between now and the end of 2014, but there are fears that some may decide to follow the lead of French President Francois Hollande, who has promised to withdraw French forces from Afghanistan by the end of this year.
Former U.S. diplomat Heather Conley, who is now director of the Europe Program at the Center for Strategic and International Studies (CSIS), says she doesn't foresee discussion of major adjustments to the exit strategy forged in Lisbon two years ago. But she acknowledges that the matter isn't entirely settled.
"I think what you're going to see is a clear reaffirmation of the transition strategy until 2014. A lot of questions still remain about...Hollande's removal of French forces by the end of this year, whether that will have any domino effect, if you will, on other European or coalition partners deciding to transition a little earlier than previously anticipated," Conley notes, "but getting to that end state and furthering the post-2014 national force will be very, very important."
??In Afghanistan, officials are adopting a wait-and-see attitude. A spokesman for President Hamid Karzai's government, Siamak Herawi, said the goal of the Afghan delegation in Chicago was to return home with assurances that the NATO allies won't abandon the fragile country.
"We hope that with the support for the programs and [proposals] that the Afghan delegation will present in the meeting, there will be a long-term guarantee for peace and stability in Afghanistan so that Afghan people can have hope in the future," Herawi said.
White House national security adviser Tom Donilon, told reporters in a presummit briefing that Obama would hold a private meeting on May 20 with Karzai in Chicago before the summit begins in order to lay the ground for wider discussions on the transition.
NATO's Future In Discussion
Although Afghanistan will dominate the summit agenda, NATO leaders will also discuss European missile defense, which has long been a point of contention with Moscow. Russian President Vladimir Putin's decision to skip the summit is being attributed to his opposition to specific aspects of the shield.
Rasmussen said progress in developing the system will be announced at the summit. "In Chicago, we will declare an interim capability. This is only a first step, but it is significant," he said.
"We are acquiring allied ground surveillance, which uses drones to provide crucial intelligence surveillance and reconnaissance information to our forces. This will help fill a gap shown by our operations in Libya and Afghanistan."
Also up for discussion is the future role of the 63-year-old alliance, which is in the midst of reshaping itself in the face of rising global threats and austerity pressures on military spending in Europe.
Leaders plan to endorse a strategy of "smart defense" -- an approach to dealing with 21st-century challenges such as the quickly shifting political situation in the Middle East and China's formidable strength. According to Stephane Abrial, the NATO supreme allied commander for transformation, the strategy involves more collaboration on military education, training, and exercises, and the application of new technologies.
What won't be on the Chicago agenda is enlargement, which means aspirant countries Georgia, Macedonia, Bosnia-Herzegovina, and Montenegro will go home empty-handed.
Once a top priority for NATO, expansion is now far down on the list of priorities, in part because of the alliance's current identity crisis but also because of objections by key members such as Germany.
Conley of the CSIS says the fact that countries are waiting in the wings to join is "very difficult" for NATO, which has always had an open-door policy. She believes that policy will be reinforced in Chicago, but little more will be offered because "there's an increasing level of frustration that the NATO enlargement strategy has run out of strategic vision."