For some 400 years, the world’s leading states pursued security by preserving the balance of power. But since the end of the Cold War, the idea has been strangely absent. Paul argues that the idea of a balance of power is not dead; it has simply taken new, more peaceful forms, which he calls “soft balancing.” This seems to have been largely driven by economic interdependence, which has made it more costly for great powers to disrupt markets by splitting the world into competing blocs. The modern global norm of territorial integrity and the availability of nuclear weapons both serve to deter great-power aggression and make balancing less necessary. And the creation of international institutions has given the United States and China ways to signal their restraint and thus dampen the worries that might otherwise push other countries to balance against them. U.S. President Donald Trump’s “America first” strategy and China’s growing military power will put his thesis to the test.