More than 50 world leaders were gathering in Chicago for one of the biggest NATO summits in history on Sunday aiming to hammer out a unified exit strategy from Afghanistan after a decade of war.

It is the first summit of the 28-member North Atlantic Treaty Organization on U.S. soil in more than a decade, and follows a two-day summit of G8 leaders hosted by Obama in the seclusion of Camp David, Maryland.

In a sign of heightened tensions, authorities in the Windy City, already bracing for massive protests, charged three men Saturday with plotting to attack Mr. Obama's campaign headquarters and other targets during the summit.

Despite a myriad of issues facing the 63-year-old organization founded in the wake of World War II as it confronts shifting 21st-century realities, the Chicago summit is set to be dominated by Afghanistan.

According to The New York Times, Obama will announce at the gathering what he has already told the leaders in private:

All combat operations led by U.S. forces will cease in the summer of 2013, when the United States and other NATO forces move to a “support role', whether the Afghan military can secure the country or not.

Among the world leaders at the table with Mr. Obama will be Afghan President Hamid Karzai and his Pakistani counterpart Asif Ali Zardari, who accepted a last-minute invitation to attend.

Despite the stubborn Taliban insurgency, war-weary international forces are seeking to hand control of security to Afghan forces while withdrawing some 130,000 foreign combat troops by the end of 2014.

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