Few periods are as instructive as Pax Romana (Latin for "Roman peace.") It was the long period of relative peacefulness and minimal expansion by the Roman military force after the end of the Final War of the Roman Republic and before the beginning of the Crisis of the Third Century.
This is the story that famed historian Adrian Goldsworthy tells in in Pax Romana: War, Peace and Conquest in the Roman World. It’s a story particularly instructive today.
My conversation with Adrian Goldsworthy: