The Kaled Dome was the home city of the Kaled race on Skaro. The Thals, their enemies, lived in the Thal Dome across the Wastelands. The dome held thousands of Kaleds, sheltered from the biological warfare fallout above ground that was causing both races to mutate. Buried underneath the dome was a bunker, the base of Davros and the Kaled Scientific Elite.
After the elites opposed his plan to make their war weapon-induced mutations reach a final form that would only know the emotion of hate and kill every other species which stood against them, Davros sold out his own race to the Thals and allowed them to fire a missile on the dome. When the Thals launched their missile, the bunker was unharmed but the entire Kaled dome was destroyed, killing off nearly every Kaled in existence, while the remaining survivors were slain by Davros's creations, the Daleks.
However, the Daleks refused to acknowledge any species which wasn't a Dalek as their superior, and rejected Davros as their leader. They continued murdering Kaleds against his wishes, until he was the only one left. The Daleks then attempted to kill him as well. (TV: Genesis of the Daleks)
Though his primary life support was knocked out by their attack, Davros's undetected secondary life support system spared him from death and slowly healed his wounds while he went into a catatonic state in the interim. The Daleks, believing he had died, abandoned him in the dome. Thousands of years later, the Daleks returned to find Davros (whose destroyed tissue had been regrown while his body was in suspended animation) in the hope he could reprogram their battle computers to win the Dalek-Movellan War. Using a combination of robot drills, explosives and slave labour, they retrieved him. (TV: Destiny of the Daleks) The Dalek Prime claimed that this event was staged on a planet called Antalin as part of a plot to trick Davros and the Seventh Doctor into destroying Antalin and not Skaro. (PROSE: War of the Daleks)