13. Order 66 (Star Wars: Revenge of the Sith)
Order 66 (also known as Clone Protocol 66) is a huge moment in Star Wars history. Palpatine ordered the mass execution of the Jedi Order. There was a protocol that was dormant in the Clone troopers until Order 66 was given. This would allow them to turn on the Jedi they had been fighting alongside during the Clone Wars. Since they were programmed to act on it, they had no idea what they were really doing or why. All they knew was that they had an order to carry out.
The Sith made sure that they had a way to weaken the Jedi Order in a way that no one had before. There were some survivors, but most of them were lost during this time. Anakin killing younglings was already bad enough, but this just amplified that by trying to kill off every single Jedi.
Obi-Wan Kenobi, Yoda, Ahsoka Tano and Caleb Dume (Kanan Jarrus) were all able to survive. Even though Ahsoka had left the Order, she was still a target but managed to fake her death in order to continue on. This was a huge decimation of the Jedi and it will forever be one of the most brutal and shocking moments in Star Wars history.