This another point about WoW's writing in recent years that is bullocks.
There is no world in which the Alliance "run out of manpower" before the Horde does. Most of the Alliance is made of up kingdoms that possess dense city populations supported by vast swathes of farmlands. Stormwind, Kul'Tiras, the Bronzebeards, the Wildhammers, the Dark Iron Dwarves (farming on soil in the Burning Steppes enriched by the volcanic ash), the Gnomergan and Mechagon gnomes, and the Night Elves.
Meanwhile, the vast majority of Horde races are relatively small tribal populations that don't even practice agriculture, capping the maximum number their populations can grow to.
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Everything points to Alliance forces being at least 10x the size of Horde forces. Even if every Horde soldier suddenly became an ace who could kill 9 Alliance soldiers per 1 Horde soldier, the Horde still loses. And that's not taking into account the vast technological and industrial superiority the Alliance has over the Horde. Machine guns, bombing campaigns, blockades, etc. Put really, the Alliance shouldn't really need to fight the Horde in the first place. The Alliance have the agriculture and the logistics to supply a long campaign. The Horde do not. Realistically after a few months, the Horde forces (and their people back home) should be starving.
Sorry. I know the Horde is cool and all (that's why I played one!), but let's not kid ourselves.
This is Japan vs the United States. It's a fight that was doomed from the start. The Horde are screwed on every possible level - manpower, food, technology, logistics - that there is just no way they can win, even if they manage an insane kill ratio. Talanji and the Mag'har Orcs who beat their chests, wanting to go to war with the Alliance in Shadows Rising, are morons.
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