Blizzard have reported that World of Warcraft: Battle for Azeroth sold 3.4 million copies on day one. The company started boasting without any figures back in May, but it turns out that this is WoW's fastest selling expansion to date.
Things were already looking up for World of Warcraft: Battle for Azeroth back in May 2018 when Blizzard's executives revealed the expansion is selling in higher-than-anticipated numbers. Strong day one sales kicked in on 14 August 2018 and people weren't shy to shell out $49,99 for standard or $69,99 for digital deluxe edition which contained cosmetic bonuses.
According to Blizzard, Battle for Azeroth is one of the fastest selling PC games of all time but they didn't provide exact sales numbers to confirm this claim. It's also interesting how Blizzard dance around the terms expansion and game, as this is indeed an expansion and not a game. On the other hand, due to the changed sales policy where you get all previous expansions with just subscribing, they have some sandy grounds to claim they are selling an actual new game.
Blizzard's CEO and co-founder Mike Morhaime stated that "Battle for Azeroth is a definitive chapter in the Horde and Alliance conflict" and that it was "thrilling to see players representing their factions in record numbers". I believe it was indeed thrilling, as that representation is directly tied with the game's revenue.
That said, Battle for Azeroth wouldn't be selling like crazy if it weren't for Blizzard pulling the right moves to give fans what they want. Horde and Alliance have been co-operating against bigger threats ever since Wrath of the Lich King, with a minor kerfuffle here and there, and it was time to return to grass roots when the factions were keen on exterminating each other.
Reigniting the conflict between them wasn't the only thing that brought players back though, as this expansion brings more new or altered playable races than any before. With the new races came new interesting situations as well, since the factions could never communicate in the same language before the introduction of Void Elves on the Alliance side, who can understand Blood Elves and vice versa.