Pax Americana

Simply put the Roman Republic, Roman Empire, and Byzantine Empire < early stages of the latter> were really the first time in human history where the majority of humans on the planet were not worried about being exterminated by the people one valley over to the left if they ever made contact. From about the time Sumer became a going concern, there were enough people concentrated to the point that actual warfare was plausible.

So from the region of Iraq to Egypt on today's map, you had city states at war. And the war was continual and increasingly the focus of more an more peoples. People tended to build up a local population, then kill the next door neighboring city state. It really wasn't until the Republic of Rome began expanding that the largest concentration of people on the globe- i.e. Mediterranean/ Near East were actually living at "peace" By the time of Imperial Rome, unless you lived way far out on the borders of the far North, if you lived within Rome or one of its vassal states, you had a reasonable expectation of living well into your early 70's.

Of course if you lived outside of Rome your life expectancy was only 30 odd years even if you were lucky enough to live in the more advanced Chinese city states or the more laid back principalities of the Indus Valley.

Prior to Rome's dominance, people who lived in the territories that eventually made up Imperial Rome had life expectancies of middle 30's at best for males and late 20's for females on average. Once you had Rome as your overlord you tended to be able to survive as a civilian. After the fall of the Western Empire, life expectancies in the former Roman territory dropped back to what it had been before the Roman Republic. Same thing happened with the Eastern Empire. As it contracted in size, those that lived outside its territories suffered a precipitous fall in life expectancy.

So the Pax Romana can be accurately determined by simply looking at life expectancy. For a very long time even before Rome ruled the world, the Romans had substantially longer lives than their neighbors. The expansion in physical territory combined with the explosion of populations as they came under Roman rule marks the beginning of the Pax Romana. The end can be determined by reversing the standards.

Being fair, Rome had a PAX that lasted at least 300 years. A fairer argument would be that the Pax lasted at least 600 years for the majority of people living from Gibraltar to the borders of India & from the Baltic Sea to the northern limit of the Saharan Desert. Compared to what came before and after, the Pax was most definitely a "peace" It would be almost 700 years before a majority of the world's population enjoyed Roman standards of life expectancy under Pax Britannia. That doesn't mean the people who benefited from the PAX in both instances were either Roman or British.

What it means is that the influence of any particular Pax often is greater and longer than the geographical and temporal extant of a leading power. Gibbon may have judged Rome to be at its zenith for 200 years, but the actual impact on peacefulness lasted far longer.

With the collapse of Rome the effects of the Pax evaporated. Then again when the Pax Britannia collapsed we had two World Wars that made the Napoleonic Wars look like a nursery game. You have to wonder that if we are indeed in a Pax Americana, and that when a Pax collapses it is followed by an amazingly intense period of open conflict and plunging life expectancies as a universal rule of human history----what will the post Pax Americana world go through before the next great power?