Originally Posted by
Frozen Death Knight
At least in the 2nd War there were good reasons why the Horde was able to do so. They pretty much had full control of the southern parts of Eastern Kingdoms with all its resources as well as them having the Blood Curse, Gul'dan's Warlocks/Death Knights, and allies like Forest Trolls to be able to push the Alliance of Lordaeron into a corner. Not to mention the strong leadership they had under Orgrim Doomhammer.
Though, that was then, and now is a completely different picture altogether. The Alliance simply is not the pushover they were as the Human Alliance. They have a huge variety thanks to the current Alliance where Night Elves, Draenei, Worgen, and even Pandaren are a part of their ranks. Whatever the Horde has, the Alliance should and can match it.