Star Wars has explained why the Empire inevitably transformed into the First Order. When Darth Sidious ascended to become Emperor of the galaxy, he clearly envisioned himself reigning forever. He worked hard to ensure every trace of the Jedi was erased from the cosmos, commissioning Darth Vader and his Inquisitors to hunt down any Order 66 survivors. Meanwhile, he devoted significant time and attention to learning to conquer death itself, in order to ensure he would never die.
Alexander Freed’s Star Wars novel Victory’s Price reveals just how pervasively corruptive the Empire really was. Palpatine deliberately created a system where it was impossible for even an ordinary civilian to live without becoming complicit in corruption at best, atrocities at worst. He had a huge chunk of Coruscant’s undercity transformed into a powerful computer to analyze every individual’s actions, in order to keep a record of their complicity. And this subtly explains why the Empire was not so easily defeated.
Palpatine’s approach ensured the dominance of the dark side of the Force, because he had created a system where every single person was forced to make everyday decisions steeped in darkness. It fits perfectly with comments from Lucasfilm’s Dave Filoni about balance, who explained every individual must choose light or darkness – not just a Force-sensitive. “The Force naturally exists in balance,” he explained. “That balance is thrown out when someone chooses to give in to their fears and then spirals out of control making selfish choice after selfish choice. Fear leads to anger, anger leads to hate, hate leads to suffering.” It also means there were far too many people who were complicit in the Empire’s atrocity, who had justified the deeds they had committed to themselves, and who would find it almost impossible to acclimatize to the New Republic. Thus the Empire’s return – as the First Order – was inevitable.
The Emperor went one step further when he initiated Operation Cinder, manipulating loyal Imperials into committing brutal acts of genocide across the galaxy. This scorched-earth policy ensured the hard-core First Order were worse than the Empire, because this served to refine the Empire down to Palpatine’s most loyal and committed soldiers and commanders. After Operation Cinder, the only ones left would be those who had participated in unspeakable horrors; anyone with a conscience would have defected. And these fanatical, immoral loyalists were the ones who founded the First Order.
But Palpatine had made one major miscalculation; there was a generation between the fall of the Empire in Return of the Jedi and the rise of the First Order. This meant an entire generation grew up without the Emperor’s direct influence, free from the shroud of the dark side. Furthermore, the New Republic chose to grant amnesties of some kind to most Imperials, and it is highly likely many learned to put the past behind them. And so, when the Resistance sent out a mayday in Star Wars: The Rise of Skywalker, the entire galaxy responded.