Again Slavery is not an Alliance. Do not even bother to compare the two, no matter how you stretch it, it simply false. Every chance given the majority of the Orcs have proven they are more than willing to embrace war, genocide and imperialism. No other current race/culture of playable characters (with the exception of the Forsaken, and we know their deal) actively participates in this. Their culture is based around Honor in Battle with a side of Shamanism.