Under which leader did the Pax Romana begin to stabilize Europe?

Pax Romana, (Latin: “Roman Peace”) a state of comparative tranquillity throughout the Mediterranean world from the reign of Augustus (27 bce–14 ce) to the reign of Marcus Aurelius (161 –180 ce). Augustus laid the foundation for this period of concord, which also extended to North Africa and Persia.

operation overlord was the codename for the battle of normandy, the allied operation that launched the successful invasion of german-occupied western europe during world war ii. the operation was launched on 6 june 1944 with the normandy landings

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.