Allow me to introduce you to:
-The First War retcons
-Second War retcons
-Illidan retcons in TBC
-The Old Gods and their entire existence
-Sargeras' entire backstory
-The Draenei
-The Demons from WC2/WC3 to TBC
-The Void's story
-Northrend going from all undead and icey to...well...y'know
And so much more