In his inaugural address, President Barack Obama challenged governments "on the wrong side of history" that "we will extend a hand if you are willing to unclench your fist." During his first year in office, he reached out to Iran, Russia, Cuba, and other adversaries. In How Enemies Become Friends: The Sources of Stable Peace, Council on Foreign Relations Senior Fellow,  explores when and how rivals are able to find their way to peace, arguing that "accommodation, not confrontation, is essential for successful rapprochement."

He challenges the claim that democracy is necessary for peace, demonstrating that "nondemocracies can be reliable contributors to international stability." Thus, "the United States should assess whether countries are enemies or friends by evaluating their statecraft, not the nature of their domestic institutions." In a related article in the March/April issue ofForeign Affairs, Kupchan argues that Obama confronts the double challenge of securing the cooperation of recalcitrant regimes while also facing considerable domestic opposition to the accommodation of adversaries. "Washington will have to conduct not only deft statecraft abroad but also particularly savvy politics at home," he writes.

Case studies in the book include the onset of the Iroquois Confederation in the 1400s, Anglo-American rapprochement in the late 1800s, and reconciliation between Brazil and Argentina in the 1980s.

Kupchan also underscores that efforts at rapprochement often fail, requiring that they be pursued cautiously. He addresses the breakdown of amity through historical cases such as the U.S. Civil War, the expulsion of Singapore from Malaysia in 1965, the collapse of the Concert of Europe after 1848, and the demise of the Sino-Soviet alliance after 1958.

Kupchan concludes that commercial interdependence plays only an ancillary role in reconciliation. "Deft diplomacy, not trade or investment, is the critical ingredient needed to set enemies on the pathway to peace."