Over the past 150 years, peaking powers—great powers that had been growing dramatically faster than the world average and then suffered a severe, prolonged slowdown—usually don’t fade away quietly. Rather, they become brash and aggressive. They suppress dissent at home and try to regain economic momentum by creating exclusive spheres of influence abroad. They pour money into their militaries and use force to expand their influence. This behavior commonly provokes great-power tensions. In some cases, it touches disastrous wars.

This shouldn’t be surprising. Eras of rapid growth supercharge a country’s ambitions, raise its people’s expectations, and make its rivals nervous. During a sustained economic boom, businesses enjoy rising profits and citizens get used to living large. The country becomes a bigger player on the global stage. Then stagnation strikes.

Slowing growth makes it harder for leaders to keep the public happy. Economic underperformance weakens the country against its rivals. Fearing upheaval, leaders crack down on dissent. They maneuver desperately to keep geopolitical enemies at bay. Expansion seems like a solution—a way of grabbing economic resources and markets, making nationalism a crutch for a wounded regime, and beating back foreign threats.