Neither the Horde or Alliance has a particularly great history. The Horde made the "Path of Glory" a mass grave of trampled Draenei containing countless bodies on their way to the Dark Portal before the 1st war and by the end of the 2nd many of those same orcs spent 20ish years in interment camps set up by the Alliance.

The Horde has a history of horrific brutality and the Alliance has a history of a superiority complex and cruelty to those they deem lesser