The Sith Empire Crusades

The Sith Empire Crusades, or the Sith Crusades, was a six-year-long period in which the Sith Empire slowly began taking control of the galaxy.

History
Some consider the Sith Crusades to have started almost fifty years prior to 100 ABY when Darth Malgus began recruiting Force users to his cause.

Raid on Sundari
Following the Treaty of Peace, the Sith Empire revealed themselves to the galaxy when a conflict between Federation and Sith forces erupted in the Sundari Assembly. The attack was a defeat for the Sith, however, it spread fear into the galaxy.

Invasion of the Galactic Government
after six years of building up their armies, the Sith simultaneously attacked Mandalore and Byss, catching them completely off guard, despite their preparations, and defeated both the Federation and Triumvirate.

Battle of Polis Massa
The Battle of Polis Massa marked the end of the crusades, as the Federation was destroyed.