The Holocaust

On a night like every other on Coruscant, a dark force gathered. Galten Varo-Kressh, ancient sith lord and leader of the avatars, would have his way with the planet, once again.
This time, however, he had a goal preset in mind. The destruction of the senate...for unknown purposes, he wished to destroy the republic's heart, and nothing could stop him.
Several jedi attempted, along with exiles and all sorts of force users. However, none proved much of a challenge, and Galten was able to best them all. Eventually penetrating the building itself, Galten lit the entire Senate aflame, incinerating all inside. The Holocaust had begun, and more than half of the senators died, the other half being evacuated prior...
The intense heat, however, had another effect. The spell would soon alter core temperatures on Coruscant, in the process altering the surface. Volcanoes, tsunamis, earthquakes, and other natural disasters would soon follow the abnormalty in Coruscant's core. Galten promised the destruction of Coruscant was imminent...
...And he was right. Coruscant was doomed, none could stop the Abyss the Great One had created...that is, but Galten himself. Once again, the avatar spared Coruscant and called off the attack. Once more, for reasons unknown, Galten spared the planet.
But not the senate. The lone casualty in all these events was the senators and the other inhabitants of the building...
May their souls rest in peace. 
The Holocaust of the Senate