with their own manpower? the factions enter an armistice exactly because the alliance could not "subjugate" the horde yet again, they don't have power to impose or demand shit, the horde also freely gave the places they took because they wanted, not because they were forced.
Again, even if there is a delusional scenario, where the alliance can try to take just the orcs, the Orcish troops would never, ever be ok with being "captured" by the alliance, as this will just bring flashbacks of being slaves and the camps, and no, the taurens and trolls will not stand aside while the alliance do as they place they hate the alliance as well.