Galactic Republic
The Galactic Republic, often referred to as simply the Republic, is the name of the interplanetary State used in the fictional Star Wars universe prior to the establishment of the Galactic Empire. The form of this government, ruled by the Senate, was introduced in the prequel trilogy. By the time of the original trilogy, it is referred to as the Old Republic. It was a democratic, though eventually ineffectual, constitutional republic tied up in layers of bureaucracy.
The Republic, as it was commonly known, was a republican government that was able to sustain itself for over twenty-five thousand years.
History
The Republic itself was formed in 25,053 BBY (Before the Battle of Yavin) when the first "Galactic Constitution" was signed on Coruscant, after the Corellian Hyperdrive connected many worlds in the Galactic Core. Whether this means that Coruscant was the original homeworld of humans or simply the most powerful world at the time is still up for debate, and there has been little said about the event other than that it occurred. The Republic was made up of several hundred thousand worlds.