The Decimation War was the name given to a two-month long conflict that virtually destroyed all organized civilization in the galaxy. The main four forces were the armies of the Republic allied with the Jedi, the new Mandalorian armies the Empire, and the Sith Order. Each had used the last millennium of peace making new technological discoveries and nursing the wounds of their troubled past. Each had built up great armies, and waited for the chance to use them. After a small conflict started a small battle between Republic and Imperial forces, they launched their new powerful armies at each other. This escalated into a declared war between the Republic and the Empire. The Mandalorians saw their chance to fight the galaxy again, as they had rebuilt their clans. The Sith Order also launched an attack with their renewed ranks aiming mainly at the Jedi, but killing any in their way. Other planets joined in the fighting on their preferred sides with their own wars, or used this conflict as an excuse to launch wars against other planets. Crime syndicates launched their own armies at whatever weak target they could find. Nowhere in the galaxy was safe.
This main battle of the war came to be known as the Great Battle, which lasted for a month. In this month, the galaxy was in total chaos. The many forces clashed in different locations across the galaxy in space and ground. Uncountable numbers died each day across the galaxy. Planets were destroyed, civilizations went up in flames. None of the major forces could gain an advantage over the other, as all had similar numbers in men and power. After a month of nonstop fighting, the galaxy suddenly became silent. All the warring parties were gone. Once heavily populated planets were now dead. The Senate building was demolished. The Jedi Temple in ruins. The Mandalorian camps lay silent. The Imperial capital was empty, the Emperor dead. The Sith master was nowhere to be found. And the temples on Korriban lay silent except for the wandering Sith Spirits.
Not everything was dead, however. Some planetary governments remained. But none were allied under a banner. Jedi and Sith remained, but were lost and broken. What would follow would be wars between planets, where one would try to conquer another. While one Jedi set on a task to rebuild a galaxy-wide union from the broken planets and reestablish the Jedi Order.