A look at the main issues for the NATO alliance at the summit meeting for heads of government in Chicago on Sunday and Monday.
An alliance formed in 1949 to deter Soviet aggression. The central principle is that an attack in Europe or North America against any member is an attack against all. The alliance has grown to 28 member nations, ranging from the United States, Britain, France and Germany to former Soviet bloc countries such as the Czech Republic, Hungary and Poland. Albania and Croatia are the newest members
The summit will affirm the shift in NATO's military mission in Afghanistan from a combat role to an advisory role next year, and on plans to help underwrite the Afghan military after the NATO-led military mission ends two years from now. NATO is pledging to maintain a multinational combat force in Afghanistan until sometime in 2014, with a firm deadline to end the mission by 2015. NATO nations, along with others such as Australia that participate in the NATO-led mission, have planned a gradual withdrawal of combat forces ahead of that deadline.
The election of Socialist President Francois Hollande in France complicates that agenda. Hollande campaigned on a promise to pull French troops out of Afghanistan by the end of this year _ two years early.
Public sentiment in Europe and the United States favors a faster pullout than NATO now plans. The United States and Britain, which have the largest forces in Afghanistan, are trying to avoid a rush to the exits by other partners.
The summit will also showcase efforts to get firm financial commitments for support of Afghan forces. NATO argues that even the projected bill of about $4 billion annually is cheaper than the cost of war. But some European governments apparently have neither the budget nor the will to keep paying. The United States expects to pay much of the cost but U.S. officials say Washington cannot foot the bill alone.
Most alliance members have endured economic reversals that make any major new defense spending unappealing or impossible. The alliance is laboring under the weight of outdated or incompatible equipment, and suffers major gaps in military capability that the better-equipped and better-funded U.S. military often has to fill. Some of those shortfalls were on display during last year's successful NATO air mission in Libya.
Former Defense Secretary Robert Gates rattled NATO when he said the alliance risked falling apart if it continued to leave the hardest fighting and biggest bills to the United States.
The alliance will declare that it has partly completed a missile defense shield for Europe. The system has achieved "interim capability," against possible missile threats from Iran or elsewhere, NATO claims. Russia opposes the system, and has rebuffed NATO efforts to form a partnership.
Russian President Vladimir Putin is not attending the summit, largely because of the missile defense split.