Via Varaks and The Inner Circle, as should be obvious I'm a big DA fan hence this post.

Book 9 seminar care of Garro. Thramas Crusade. Full scale war across a swath of space...Chondax, even Signus etc... are campaigns, but Thramas is a war in terms of scale. The First Legion is the most powerful fighting force in the galaxy for quite some time essentially until the rise of the Ultramarines and centuries of attrition finally set in. Full list of Dark Mechanicum. Additional details on Night Lords.