A young Jedi named Starkiller helped the Empire hunt down and destroy the Jedi Knights
—Obi-Wan Kenobi talks about the Purge to Luke Skywalker
The Great Jedi Purge, also known as Palpatine's Purge and the Second Jedi Purge, referred to the efforts initiated by the Sith Lord Darth Sidious upon his creation of the Galactic Empire in 19 BBY to eradicate the Jedi Order. It resulted in the near-annihilation of the Jedi, as it had been with the First Jedi Purge that occurred after the Jedi Civil War in 3,956 BBY. The purge officially began with Order 66 following a botched attempt by Mace Windu and three other Jedi to arrest the chancellor. The order declared the Jedi enemies of the Galactic Republic and ordered the Grand Army of the Republic to turn on them.
Sidious, now Emperor of the Galactic Empire, used Darth Vader, Starkiller and other agents of the Empire to hunt down and kill the remaining Jedi. Some Jedi fought the Empire until their deaths, like Roan Shryne and those at the Conclave on Kessel. Others hid from the Empire, like Obi-Wan Kenobi and Yoda. In the nineteen years that followed Order 66, many Jedi fell to Vader, Inquisitors, Emperor's Hands, and even bounty hunters. By 1 BBY, such a small a number of Jedi remained that the Emperor, considering the Jedi to be no longer a threat, put an end to the Purge.