The new RTS is Dawn of War based (Warhammer 40,000) isn't it? An expansion. While the MMORPG is based on Warhammer.
There's Warhammer and Warhammer 40,000. The first based on ancient times (elves, dwarves, orcs, wizards, etc) and the latter based in the future.
Dawn of War will provide information on the Warhammer 40,000 world, while Mark of Chaos will provide information on the Warhammer world.
There are quite a few other games based on these two games but the ones I've mentioned are the most up to date.