Originally, Draenor was a planet with a nigh-uneventful history until a series of progressively more incredible and unusual events, brought to the world from outside sources, plunged it into chaos. According to what we knew -- which was admittedly very little -- the orc clans of Draenor had no issues with the rest of the world, or with each other. There may have been the occasional squabbles between clans, but there was nothing remotely resembling full out war ... at least nothing that's been recorded in history as we know it. However, the announcement of Warlords of Draenor seems to indicate a big history lesson is on the way.
Draenor's history, one distinct moment in time has been altered, creating a separate fork -- a bubble of time, if you will -- that has changed the fates of these old heroes. So who are the Warlords of Draenor? We have their names. What we don't have is the new history revealed in the expansion just yet. But even in the original timeline, these orc warlords each had different, unique histories that all tied in together, courtesy of the Burning Legion's meddling and influence.