Values-based defensive alliances are valuable. They support mutual security, creating political space and incentive for profitable economic and cultural exchanges. Most important of all, such alliances help to deter potential and, where necessary, defeat adversaries in armed conflict.

NATO is the most successful defensive military alliance in history. It greatly benefits Americans. But alliances require more than shared values and interests. To retain the credibility of democratic populations and governments, alliances require fair burden sharing. NATO continues to fall short here.