The Jedi Rebellion was a civil war fought between the Jedi Order and the followers of Han Rammar. It began when Rammar tried to destroy the Jedi and Senate and claim the Galaxy as his prize.
After he ordered the execution of all the Senators, Rammar moved on the Jedi Order. However, Admiral David Jesseson was not willing to carry out his orders and bombard the Jedi Temple of Yavin IV. Rather he prevented another fleet from carrying out his orders.
The Jedi then met up with Jesseson and retook the capital, establishing the Jedi Theocracy.