There is, unfortunately, no easy fix. After losing more lives in World War II than the United States — and many, many more in World War I — our historic allies have very good reason to fear international conflict and renewed militarization. Moreover, we cannot dictate defense policies to sovereign nations. We should and must try to persuade, and we should and must demonstrate to them that our own security umbrella cannot always be sufficient to protect their national interests nor is it sufficient by itself to protect an international order so carefully constructed to avoid future Great Power clashes. I fear, however, that only the hard lessons of real power will teach our allies that they must once again demonstrate strength of will to resist aggression.

It would be foolish for the West to court armed conflict over Ukraine, but it is similarly foolish for our oldest allies — powerful nations — to choose impotence. History has demonstrated that voluntary weakness is ultimately far more costly than conviction backed by prudently used economic and military strength. Just as Britain and France chose to be weak, they can now choose to be strong.

Whether by wise strategic choice, public and political exhaustion, or sheer recklessness, America will not always take the lead. Why can’t our allies fill the vacuum?