After the Battle of Ithor, Darth Admer decided that Onderon has a potential of becoming a major staging area for the sith empire, and called an invasion to the world. After a harsh and victorious space battle, the planet fell under a crusaders' blcokade. Under the dark lord's influence, the local population rebelled against the Jedi, and the planet fell to Mandalorian hands. After it's fall, Admer visited Freedon Nadd's tomb and achieved an even greater knowledge of Sith Sorcery, which allowed him to increase the mandalorian's war efforts against other republic forces.