"For most of the history of the Galactic Empire, Kalgan was a semi-tropical resort world, 7,000 parsecs from Terminus and about 3000 parsecs from Trantor. Despite the breakdown of the Empire, Kalgan continued its prosperity under the rule of a series of princes.
Kalgan was one of the first planets taken over by the Mule in his string of conquests. After he defeated the Foundation, the Mule made it the capital of his Union of Worlds. After the Mule died, Kalgan was ruled by a series of First Citizens from Han Pritcher to Stettin. The last of these, emboldened by the legacy of the Mule, launched a war against the Foundation. After the war ended in the defeat of Kalgan, the Kalganian Navy was dismantled, and the 27 worlds remaining in the Union were allowed to vote for return to the Union, full independence, or entry into the Foundation union."
(Information from Wikipedia)