One of the reasons that Deep Space Nine was my favorite of the post Original Series Star Trek is that the writers got to make some pretty bold moves. One of the boldest and most insightful, I feel, was their choice of what to do with the Mirrorverse from one of the Original Series’ strongest episodes.
In the Mirrorverse, the Federation was the Terran Empire: a bloodthirsty, dictatorial and ruthless state. And Vulcans were pretty much Romulans. During their brief sojourn in the Mirrorverse, our own universe’s Kirk tried to convince the Mirrorverse’s Spock to try overthrowing the Terran Empire in favor of a Federation. In DS9, we got to see the results.
Turns out that Mirror Spock had been quite successful at the overthrowing the Empire part. Unfortunately, that merely left the Empire in enough trouble that its subject peoples plus the Klingons and Romulans had easily conquered Earth and made humanity into a slave race. And they were still enslaved about a century later.
The Original Series had made an unwarranted assumption, and it is one that uneducated “revolutionaries” make to this day: that when an oppressive system is toppled, freedom and justice will naturally follow. They do not. To establish them requires hard work, and it is not often hard work that the “revolutionaries” are equipped to do. To take a few examples, it must have seemed to the Aztecs’ subject races that the Spaniards — whose God, notably did not demand human sacrifice — were their liberators. The French believed that toppling the nobles, and later the king, would bring them equality, liberty and brotherhood. What they got was the Committee Of Public Safety, the Reign of Terror, and Napoleon. Aleksandr Kerensky had a chance to establish a Russian Republic when the Czar’s oppression was overthrown, as did Yeltsin when the Soviet Union fell apart. They were succeeded by Lenin and Putin respectively, and the only thing better about Putin is that he isn’t using starvation as a tool for mass murder, as far as I know.
Overthrowing oppressive systems isn’t very hard, even when it isn’t easy. Not replacing it with an enemy that’s even worse is the trick.