The golden age of the Roman Empire is often called the Pax Romana... it ended with the death of the last of the "5 Good Emperors", Marcus Aurelius, in 180 C.E. It was characterized by a lasting peace within the Roman Empire -- but a peace that was maintained only by nearly continuous warfare at the periphery.
While it is often said that history repeats itself, these cycles are not exact reproductions of the past, but rather take the form of chaotic self-similarity across scale owing to common causal mechanisms. During the Pax Romana, Rome was under increasing pressure on its borders from "barbarians". Nearly 100 years ago, Nietzsche asked "Where are the barbarians?". I think that he would consider his question answered if he were alive today. Are we now at the dawn of a Pax Americana--a lasting period of domestic peace sustained only by warfare on the periphery? Or are we at the close of that era (the Post-WWII golden age of America)?? Perhaps this quote provides the best summary, as it seems to fit well into history's self-similarity across time:
"Although things did seem to be getting better, there were problems on the horizon. Barbarian pressures were mounting. There was a considerable decline in the slave population and the army was no longer large enough to maintain the frontier."
Taken from Steven Kries' "Lectures on Ancient and Medieval European History" , it describes the state of Rome at the death of Marcus Aurelius.
On a loosely related note, if you haven't already read Michael Parenti's "The Assassination of Julius Caesar: A People's History of Ancient Rome", I highly recommend it for its insight and timely nature.