Dromund Kaas was the awesome capital of the Sith Empire. Whereas Korriban was where the Sith went to die, Dromund Kaas was where they went to live it up and party. It was sort of like Disneyland and Las Vegas and Transylvania and Bangkok and Tijuana all wrapped up into one, and somehow managing to be even more evil.
The Sith Emperor ruled from his secret headquarters on Dromund Kaas and did all his evil dirty work there during the time of the Cold War. He oversaw the construction of the sprawling Sith capital after Naga Sadow's defeat in the Great Hyperspace War. When the Sith first arrived on Dromund Kaas, there was nothing there but swamp. Everybody thought it was daft to built a capital in the swamp, but they built it just the same, just to show 'em. It sank into the swamp, so they built a second one. That sank into the swamp. So they built a third one that burned down, fell over, then sank into the swamp. But the fourth capital stood the test of time, allowing the Sith Empire to prosper. Over the centuries the planet gradually accumulated so much Dark Side energy that the native flora and fauna all died off, to be replaced with creepy Sithspawn. Various Sith cults took up residence there, including the Prophets of the Dark Side.
Dromund Kaas also became the center of various evil forms of entertainment, such as ultimate cage fighting, disco, mud wrestling, slasher films, bestial pornography, and the Academy Awards.