It wasn't only the Undead they wanted to get rid of, but also the Forsaken under Queen Sylvanas. They even wanted to create a new virus, a bio-weapon that could exterminate all Undead. That was how the world was – one's morals and decisions were based on which side they were on. The Scourge wanted to turn everyone into Undead, including the Demons, the Monsters and the Elves. The Forsaken wanted more humans to join their army. Monsters wanted to terminate both humans and Undead alike, and hopefully take out the Forsaken during the process as well. As for a player like Lu Li, his joining of the military was so that he could enjoy the benefits of receiving better missions and rewards.
"Young one, your outstanding performance will be rewarded," General Halford Rebane said to Solomon. For the first time, Solomon felt that he was finally respected by the military, and thought that Rebane would be reporting his contributions to the higher-ups.
