ca 25,053 BBY

The Galactic Republic is formed. Its capital is the planet Coruscant. Founding members include Coruscant, Alderaan, Corellia, and Chandrila.
A Guide to the Star Wars Universe; Tales of the Jedi. The exact date comes from the "Galactic Timeline" at the Star Wars: Old Republic website.
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ca 25,000 BBY
A young student of the Force named Reda Jalooz steals an heirloom of the Kashi monarchy. Months later, Jalooz learns a dark secret about the relic and asks for forgiveness. Coon afterward, a supernova destroys the Kashi system. The cause of the supernova remains unknown.
Star Wars Adventure Journal: "Relic", via Time Tales.
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The planet Kuat is discovered and settled by human aristocrats from ten wealthy shipmaking families.
Coruscant and the Core Worlds Sourcebook.
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A group of Duros colonists settle on the planet Neimoidia. Over thousands of years of evolutionary change, Neimoidians come to be considered a separate race from the Duros.
The Essential Guide to Alien Species.
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ca 25,000 - 20,000 BBY
Many of the galaxy's first starship manufacturing companies are founded, including Alderaan Royal Engineers, Core Galaxy Systems, Corellian Engineering Corporation and Rendili StarDrive.
The Essential Guide to Vehicles and Vessels.
 
 
 
ca 24,900 BBY
The Jedi Order swears loyalty to the Galactic Republic.
Galactic Timeline - Star Wars: The Old Republic website.
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