[@Hank] Please do. Like I said, the force of Chaos and the Necrons do both exist, but you need some very good justification to have them as a Legion's Hated Enemy for various reasons. There's quite a few xeno races that the Imperium might have fought against in canon at some point, and at least one other human faction built up independently from the Imperium, called [url=http://warhammer40k.wikia.com/wiki/Interex]the Interex[/url]. There is a very good chance that at least one Primarch will encounter the Interex at some point, so be prepared for that, ladies and gents.