The website unrv.com summarizes conditions from about 27 BCE to 180 CE as follows:
The Legions patrolled the borders with success, and though there were still many foreign wars, the internal empire was free from major invasion, piracy or social disorder on any grand scale.
The Empire went into decline thereafter, and eventually fell, but, at its height, Rome for the most part enforced peace in the areas it controlled.
As was the case with the Soviet Union and Yugoslavia in the 20th century, the Roman Empire combined many cultures and religions into one political entity. Those disparate peoples may well have engaged in frequent warfare, had the iron hand from above not held them in place.
That concept is sometimes applied to the USSR and its satellite nations. Moscow is said to have enforced a Pax Sovietica, that was similar to the Pax Romana.
As the Soviet Union's power waned, and eventually disintegrated, fault lines in its empire began to show. Christian Armenia fought against Muslim Azerbaijan. Minority peoples within Russia itself, such as the Muslims of Chechnya, fought for autonomy. The potential for such violence had always been there, but the iron hand from Moscow had kept those groups in check for many decades.
The Pax Sovietica also extended to the satellite countries of eastern Europe. Minority ethnic groups in many of those countries nursed grudges against their perceived oppressors.
Yugoslavia was not controlled by the USSR, after its Communist dictator Josep Broz (a.k.a. Tito) broke with Moscow in 1948. But there was a "Peace of Tito" (not being fluent in Latin, I can't translate that) that was a smaller-scale version of the Soviet Peace. Tito held together the different cultures within Yugoslavia, continuing to rule until his death in 1980.
The combination of Tito's absence, and the general air of revolution in the region, doomed the Yugoslav state, by the early 1990s. As I said here, I'm not going to go into detail but, as you undoubtedly know, the result was extremely violent in most of the territory that had constituted Yugoslavia.
Religious differences, which can paint The Other as a demonic force that needs to be dealt with accordingly, accentuated the violence.
The Communists did not eliminate nationalism within the territory they controlled. They kept a lid in place for several decades that was tight enough to prevent those pressures from exploding.
Was the eventual explosion worse than it would have been, had that lid not been held in place? That's one of those what-ifs of history that can't be definitively resolved. But the poverty and the suppression of civil society that were produced by totalitarian rule probably made things worse.