Space devil wants to kill everyone, his army is infinite, space gods create Azeroth (kinda), space gods are killed by space devil, races pop up over time across azeroth, big war between space devils army and elves, elves win but continents split apart, 10,000 years later way more races pop up humans in particular.
Meanwhile on another planet, orcs are being fucking dicks 'cause space demons, kill all the space goat people (draenei), orcs fuck the whole world up, super orc warlock Gul'Dan opens portal with help of super human mage Medivh between Azeroth and orc planet, BIG WARS HAPPEN, humans win in the end.
Arthas is doing paladin stuffs, decides to save his people from becoming zombies, turns his people into zombies instead, becomes king of zombies, fucks up blonde elves homeland. Meanwhile orcs gather together to go to another continent 'cause Medivh said so, some humans follow them, humans and orcs meet brunette elves, big fighting starts until space devils army shows up, brunette elves and Medivh are like "stahp it please" and they do, humans orcs and brunette elves kill space devils space goat friend and space devils army goes away.
Brunette elves king(?)'s brother acts all emo and goes to orcs original planet with blonde elves and fish people, space devils other space goat friend is all like "wtf bruh, this is our planet, not cool bruh, go kill zombie king for me" and brunette elves king(?)'s brother is all like "okay", zombie king beats him and emo elf goes home to orc planet.
4 years pass and nothing fucking happens.
2 factions come together to fight each other 'cause reasons, human king goes missing, suddenly dragon lady is behind it all, human king comes back, kills dragon lady, we kill fire king, dragons, cthul.. I mean C'Thun... and some zombie dude.
Suddenly portal opens to orc planet, we wage war against emo elf and his army of blonde elves, enslaved demons, fish people, ugly space goats and poser emo elves. We win, but it was only a set back, but we still win.
Zombie king is all "that was a nice nap time to destroy the fucking planet", does it in the most ridiculous way possible, almost wins and then DUH LOIT takes pity on us scrubs and lets us win.
GIANT FUCKING DRAGON RUINS EVERYTHING, orc leader turns into Jesus (or Moses if you're going by movie logic), jesus kills the dragon, other dragons are like "our purpose is fulfilled", makes no sense 'cause dead dragon got powers at the same time, worst expansion eva.
We decide to go to Pandaland, the land itself is apparently a sadist, orc leader goes crazy 'cause we need a final boss, DIS AIN'T WAT DA HURD IS ABOUT!! Everyone (and I mean everyone) fights orc hitler, orc hitler loses and is taken to Panda jail.
Time travelling dragon shows up and takes orc hitler back in time to another reality on orc planet. "TIMES CHANGE". Medivh's only friend shows up, "Collect 4986 crystals for me" "For Azeroth", Medivh's only friend is a pretty shit wizard. We stop orc hitler and super orc warlock Gul'dan who is suddenly alive. "U MAID A PACT"
Suddenly emo elf and super orc warlock are in the same cinematic together, get hyped.
TLDR; WoW's lore is too complicated.