After the events of Armageddon, Eobard Thawne finally reveals why he hates Barry so much

Arthas was forced not to travel to Northrend. Without a champion, the Dreadlords were forced to take a more personal approach to summoning the Burning Legion and it led to a chain of events where the Scourge eventually falls under the control of someone more powerful and unpredictable, Illidan Stormrage. The new Lich King uses his newfound resources to wage war on Azeroth's enemies