Seeds Of The Empire
Through political manipulation Palpatine placed himself in a no lose situation, acting as both the leader of the Republic and Confederacy, as the Clone Wars raged on Palpatine was the puppet master on both sides, sending Republic Forces into ambushes, and ordering Separatist leaders who were captured to be either imprisoned or executed. Always seeking a more powerful apprentice, Palpatine began to manipulate Anakin Skywalker, seeking to turn the young Jedi Knight to the dark side of the force as Count Dooku's replacement at his side.
Palpatine also arranged for the creation of a Clone Army through the Kamino cloners using the name of a deceased Jedi Master to avoid suspicion. This army was given a secret order that they all were programmed to obey, Order 66, an order that once they heard would trigger them to kill all Jedi.
The Rise Of An Empire
With the Jedi all but exterminated Palpatine gradually took away freedoms from various star systems, many worlds found themselves governed by martial law and infested with Stormtroopers regardless of if military assistance had been asked for or not, slowly but surely worlds freedoms were taken away, leading to a splinter group who were at first considered terrorists, and later freedom fighters called the Rebel Alliance.
The Empire initially encouraged the Alliance as a means to gather it's traitors in one single location, but the alliance grew into a greater threat, and the Empire responded by taking more power away from individual worlds by disbanding the Galactic Senate once and for all.