From the introduction:
The Jedi Order has been a constant in the Galactic Republic for over twenty-five thousand years. They act as guardians of peace throughout the galaxy, settling disputes and providing council and sage advice that can only be given through pure benevolence and deep understanding of the Force.
During the restructuring of the Galactic Republic a thousand years ago following the New Sith War, the Jedi Order willingly placed itself under the appointment to the office of the Supreme Chancellor. By the request of the leader of the galactic government, the Jedi served as ambassadors, diplomats and intermediaries to the various governing bodies of the Republic and its allies.
With the onset of the Clone Wars, the Supreme Chancellor appointed the Jedi to act as generals and commanders to the Grand Army of the Republic. During this dark time many Jedi, from master to Padawan, fought and lost their lives in the conflict.