Things fall apart; the center cannot hold. The rules, policies, and institutions that have guided the world since World War II have largely run their course. Respect for sovereignty alone cannot uphold order in an age defined by global challenges from terrorism and the spread of nuclear weapons to climate change and cyberspace....

The strategy of engagement-the use of incentives alongside other foreign policy tools to influence the behavior of difficult regimes-has received relatively little scrutiny when compared with economic sanctions or military force....