2. Order 66.
Aside from the theft of the Death Star plans and its destruction, there is perhaps no other singularly defining moment in Star Wars than Order 66. Palpatine puts his plan in motion and the clones turn on their Jedi generals, cutting them down in barrages of laser fire or blasting them from the sky.
Even Commander Cody, who fought side by side with Kenobi throughout the Clone Wars, turned on his compatriot and friend without question. The sheer brutality with which the clones emotionlessly murder the bulk of the Jedi Order in one fell swoop was nothing if not jarring.