As well everyone knows, the shiny knights of the Middle Ages were made obsolete by the invention of guns. Many also realize that with the invention of a very deadly, easy to use weapon it became much more difficult for rulers to maintain control of their subjects. It is no coincidence that governments, in particular authoritarian ones, don't last as long as they used to.
With those in mind I looked at the Wikipedia page on Roman military equipment and my suspicions were confirmed, Roman soldiers wore considerably heavier armor after Caesar took power than when Rome was a republic. Able to survive attacks that would kill someone less well protected, courtesy of their emperor, the Roman legions were able to put down peasant rebellions easily. Their successors after the empire's fall were even better suited to enforcing the will of their feudal lords. That all disappeared when the peasants became able to kill a knight at 100 paces; within a few centuries the only monarchs who hadn't been deposed were those who turned over most of their power to democratic institutions such as Britain's.
In short, when personal armor technology can effectively protect against the most commonly used weapons technology, authoritarianism thrives because armor is too expensive for the average peasant to acquire. These days most authoritarian regimes die with their first ruler. However, while the bulletproof vests given to most soldiers can be easily penetrated by a civilian hunting rifle, there have been considerable advances in personal armor tech within the last 50 years. It is possible that within a century soldiers will be nigh-invulnerable against anything short of heavy explosives.
Personally I welcome the Terran Federation and the Mobile Infantry, will be better than this democratic chaos.