What is a pax Romana, pax Britannica, and pax Americana?

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The End of Pax Americana: How Western Decline Became Inevitable

The Euro-Atlantic world had a long run of global dominance, but it is coming to an end.

https://www.theatlantic.com/international/archive/2012/04/the-end-of-pax-americana-how-western-decline-became-inevitable/256388/