I have always found the moments in the story of World of Warcraft and its expansions where the antagonists are the ones to strike a victory on the Alliance and/or the Horde and the adventurers to be far too rare.
In the great majority of the situations where there is a a theat or start of a threat the adventurers just have to pop up to beat the villains whenever they are Burning Legion, Scourge, Old Gods and their forces, villainous versions of the Horde, hostile races or local criminals.
What are the instances where the adventurers should have been beaten, and the factions suffered a true defeat or failure in the story, over all of WOW and faced true consequences and casualties because of it ?