The Great War was the war that Alric and his Nine Avataras fought in. During this time many allies joined the Light and stood against Balor and his dark allies. The Nine, along with the Dwarven King, Fir'Bolg King, Skrael King, Durak, Kyrand, and many other notable members of the Legion--joined to protect their world against the threat of Balor, the newest incarnation of the Leveler and the most deadly yet.
Among Balor's forces were hordes of undead, his lieutenants being the Shades--but not only did he have these and the Fallen Lords, but he also held warriors in his power, such as Fang Grinder, the Untamed King, and others.
It should be noted in the Myth World, that the Leveler is an evil entity that corrupts and raises former good warriors/heroes to his side. The Watcher, The Leveler, Cartuke, Skyrosh, Moytirra, Fang Grinder, and perhaps the Dark Gods are the only ones that could honestly be seen as characters that were purely evil.