Warhammer 40K's lore is riddled with warfare among factions. Which of the many sides of the conflict are the most powerful?

The Imperium is a big place and sometimes Planetary Governors and others decide they'd rather go solo. That's when Rebellions ...

Where did all the Thanatar Calix Seige-automata go in the 41st millennium? The Mechnanicus needs to bring them back with a ...