Once Kel'Thuzad was whole again, Arthas led the Scourge south to Dalaran. There the lich would obtain the powerful spellbook of Medivh, and use it to summon Archimonde back into the world. From that point on, Archimonde himself would begin the Legion's final invasion. Not even the wizards of the Kirin Tor could stop Arthas' forces from stealing Medivh's book, and soon Kel'Thuzad had all he needed to perform his spell.