Beware a world without American power

Nuclear deterrencenato works—or at least it has so far. To understand how, look at the war in Ukraine. America and Europe arm their ally but dare not deploy combat troops against Russia. In turn, Russia dares not strike at the West. Mutual terror ensures that nuclear powers do not attack each other overtly, just as it stopped the cold war from turning hot, even though plenty of proxy conflicts raged. A sign of success is that only nine countries have —fewer than once feared, and fewer than the number of states able to make them.As this week marks the 75th anniversary of the signing of the North Atlantic Treaty, thank the generosity of“extended deterrence”, by which America has sheltered European and Asian allies under its nuclear umbrella. It has done so in part to contain foes and in part to dissuade friends like Germany, Japan and South Korea from going nuclear themselves.