Rebellion Era Campaign
Following the events of the Clone Wars, then-chancellor Palpatine declared that in order for the preservation of the security and stability of the galaxy, the Republic needed to be abolished and reorganized into the first Galactic Empire.
Using the false illusion that the self-proclaimed Emperor Palpatine has no other agenda but the prosperity of the Empire, he continued to win the favour of the majority of the senators through promises of peace, freedom, justice and security.
However, a small number of senators saw the dangers in allowing one man to rule the galaxy. Palpatine was quick to dismiss and rebuke any negative claims against his rule and his government. And thus, the Sith continued to rule the Galaxy with no Jedi to oppose them.