Much of the postwar free world did not seriously concern itself with issues of national security. It didn’t have to, in a world where the U.S. was the only military superpower, its policy of benign hegemony lifted worldwide livelihoods through free trade and mutually assured destruction deterred major wars.

Shifts in the balance of power from the U.S. to China, slowing world growth and increasing income inequality have changed the calculus of war and peace. Experts now worry that other autocratic leaders will follow Vladimir Putin to pursue imperial conquest over weaker neighbors.

“We have to wake up from the dream that wars are no longer possible in the nuclear age,” says Yoko Iwama, a professor at the National Graduate Institute for Policy Studies (GRIPS).