Originally Posted by
Mahmeya
Draenor: orc manipulated by the legion
First war: orc manipulated by the legion
Second war: spillover of first war (Orgrim taking over Gul'dan)
Third war: includes orc manipulated by the legion (Nerzhul the Lich King)
Cataclysm: orc overcome by the legacy of ... orc manipulated by the legion (Grom - Garrosh)
MoP: the orc above, eventually manipulated by old gods
See the pattern? Orcs are easy to manipulate. Now, Sylvanas break the pattern, true. We're still to see her true motives.
Also, keep in mind that most of the alliance had a fair share of bad stuff happen to them, they had enough of the war and are more likely to make a warmonger among them stand on its own (Garithos, Daelin) or try to put them back in line.