@maxdancona,
Chinese history is filled with conquest and subjugation based on race as well.
The fact that sometimes one group found it convenient to ally themselves with another group doesn't prove much. Wars along racial/ethnic lines are pretty much consistent throughout history.
Our obsession with racial equality is new. For all of the wars, and subjugation and ethnic conflict, and genocides throughout history... you don't see any discussion about equality until very recently (i.e. the past 300 years).
Romans had the idea of "natio". How badly you could treat a slave had to do with where that slave was born. This was just accepted in Roman society.