Day of Black Sun

The Day of Black Sun refers to a day in history when a solar eclipse occurs, rendering Firebenders powerless. There have been two known days of black sun in history. Not much is known of the first, other than that it was called "the Darkest Day in Fire Nation History". On the second Day of Black Sun, the Fire Nation Capital was invaded, with the objective of defeating the Fire Lord, thus ending the century long war. However, the Fire Nation was informed of the invasion, because Azula, Mai, and Ty Lee disguised themselves as the Kyoshi Warriors and had the Earth King (unknowingly) tell them about the plan. Because of the Earth King's mistake, the Fire Nation was able to prepare for the invasion. The invasion force managed to reach the Royal Palace, but were unable to escape after the eclipse ended. The invasion force was taken prisoner while the younger members fled on Appa.

The Day of Black Sun was not a total failure, however. It was revealed in the finale that during the eclipse, King Bumi found "the right time to strike" and single-handedly liberated the city of Omashu, thus beginning the eventual liberation of the fire nation occupied parts of the Earth Kingdom.

Episodes

 * The Day of Black Sun, Part 1: The Invasion
 * The Day of Black Sun, Part 2: The Eclipse