End of the Clone Wars

The Clone Wars end, Count Dooku is killed by Anakin Skywalker, General Grevious is killed by Obi-Wan Kenobi, Chancellor Palpatine, revealed to be Sith Master Darth Sidious, kills Mace Windu and his Team 
Chancellor Palpatine reorganizes the Universal Republic into the Galactic Empire with himself as ultimate Galactic Emperor and Anakin Skywalker turns to the dark side of the force and becomes Darth Vader, Palpatine's second in-command and third apprentice 
The Great Jedi Purge is orchestrated by Sidious and Vader and almost all Jedi are hunted down and killed 
Darth Vader kills the Separatist leaders on Mustafar 
Luke Skywalker and Leia Organa are born to Padme Amadiala, Padme dies in childbirth, Obi-Wan, who survives the Purge, delivers Luke to Owen and Beru Lars, Bail Organa adopts Leia, these are done in order to protect them from Emperor Palpatine and their father, Vader