Sylvanas' Forces were a group of Undead under the command of Sylvanas Windrunner. After The Fall of Silvermoon, Prince Arthas Menethil transformed the High Elf Ranger-General into one of the Undead. Sylvanas was horrified and hated Arthas, but was forced to serve the Lich King. After the purge was completed, Arthas begun to suffer tremors and started losing his power. This was because the Lich King had begun losing power himself. Another result is that he begun losing his control over other undead, such as Sylvanas.