The Old Republic was a democratic interstellar government that ruled vast areas of The galaxy.
The Old Republic lasted for at least 24 000 years. The Jedi Order was known to act as peacekeepers through this period, aiding people throughout the Republic's territory. The Sith Order, as well as various Mandalorian militant groups, were known to wage war on the Republic and the Jedi through its reign.
Eventually, the Old Republic fell and the Jedi Temple on Coruscant was raided by Mandalorians. The ancestors of Pre Vizsla stole the Darksaber during this raid. 1000 years before the Clone Wars, the Sith Lords were defeated and driven into hiding. A Galactic Republic rose from the ashes of the Old Republic. This government would go on to expand through the galaxy for the next 1000 years, upholding some of the vital aspects of the Old Republic and being aided by the Jedi Order.
During the Clone Wars, Jedi Master Saesee Tinn once commented that this conflict saw battles that had not been seen since the days of the Old Republic. At this time, the Jedi Order were still using a training ship, the Crucible, that dated back to the Old Republic and had its emblem on its internal walls.