Rough Roman Memes

Explanation: In the Republican era of Rome, their foreign policy was very aggressive. We often assume 'imperialism' with, well, the Roman Empire, but this is just naming of convenience; most expansion was done under the Roman Republic. Why is that? Well, one of many reasons (as historical causes are rarely simple) is that civic pride is a prickly thing. When the people see themselves as part of the government, and the government is insulted, they feel insulted. For this reason, despite Rome not having a standing army during the Republican era, and needing a popular vote to declare war, they went to war constantly. Didn't you hear? Those filthy [insert barbarian tribe here] TROD ON the rights of a ROMAN citizen! They disrespected an OFFICIAL of the REPUBLIC! OUR Republic! That could have been me! Or you! Or our sons! Does it not make your blood BOIL?

The Principate, the early Empire, put great effort into keeping this republican facade, but under the Principate, all real power rested in the hands of the Emperor. And autocrats are less predictable and less tenacious than entire populations. An autocrat can be apologized to; populations rarely take apologies well enough to simmer their passions; an autocrat can be bribed or reasoned with; populations are expensive to bribe and can be reasoned with only slowly, as word passes from one citizen to the next - usually too slowly to prevent them from going to war. Thus, the Principate had every interest in maintaining the reputation of Rome for warlike behavior (to preserve the Emperor's political power at home), but, in practical terms, had less desire to prosecute wars to the bitter end.

By the Dominate and Byzantine periods, the Emperor was no longer reliant on the political support of the people of Rome, and so were free to make 'rational' choices, like preferring paying tribute to expensive and uncertain wars. Unfortunately for them, rational choices do not always have an ideal outcome; it was Rome's irrational level of aggression which allowed it to cow so many foes for so long, and sustain the safety of the polity. Strange how that can work. Furthermore, the sense of the citizenry's identification with the polity had been weakened by hundreds of years of shit policy, instability, and aristocratic abuses, and there was not nearly the outpouring of support against foreign foes which Rome could previously rely upon.