Read any front page, listen to any news anchor, or talk with any foreign-policy expert, and you’ll learn the same thing: Nuclear war is a real possibility. As a millennial, I find this inconceivable.

These are unpeaceful times, by all accounts. No more needs to be said about that, but notice if even that one line felt a bit stressful. Breathe. Peace is an inner experience as well as an outer ...