Serroco

Serroco was a planet that the Mandalorians used as a nuclear missile testing range during the Mandalorian Wars. Unfortunately, they purposely accidentally forgot to tell the Galactic Republic, who had a colony on the planet, about their plans. The attack was so devastating that it gave Zayne Carrick visions and made him cry like a little girl. Anyway, most people on the planet got PWN3D, and the ones that survived lived just long enough to see the Mandalorians realize their "mistake" and decide to destroy the planet to try and cover up their "mistake." No one knows what really happened because the Mandalorians PWN3D everyone on the planet.

Theories about what really happened

1. Some people think that the Mandalorians purposely bombed the planet because they wanted to kill the Republic soldiers and other Republic persons on the planet, this would make it a deliberate attack. it would also mean the second attack that killed all the survivors wasn't an attempt to cover up their mistake, but a (successful) attempt to correct the mistake of leaving people alive after the first attack.
2. Other people think the Republic hated the planet and knew about the Mandalorian attack. These people believe that the Republic did nothing to stop the attack because they wanted the planet to be destroyed. However, this theory makes no sense because the Republic might not have liked the planet, but they did like their own soldiers, they needed them to win the war. If they had known about the attack/accident, they would have evacuated their soldiers.
3. There are also people that think the Republic hated the planet and knew about the Mandalorian attack. These people believe that the Republic did nothing to stop the attack because they wanted the planet to be destroyed. Because this theory has been said to be false above, these people also say they believe that the Republic's worst and most stupid soldiers were on the planet. These soldiers would have caused the Republic to loose the war, which is why the Republic wanted them as well as the planet which they hated to be destroyed.