Deathwatch First Founding wrote:
Many Space Marine Chapters have existed for millennia, with those of the First Founding having their roots in the original Legions created to prosecute the conquests of the Emperor’s Great Crusade. With histories stretching back into the dawn of the Age of the Imperium, it is perhaps inevitable that Chapters should come to blows, both metaphorically and at times literally. There are many instances of rivalries, and some of outright hostilities. The deep-rooted and mutual antagonism between the Space Wolves and the Dark Angels is well known, but there are many more examples. One example of such rivalry can be found in the case of the Raven Guard and the White Scars, who have harboured a mutual mistrust dating back centuries. In truth, there may be no single cause of the bad blood between the two Chapters, but the mere mentioning of several battles are sure to raise the ire of Raven Guard and White Scar alike. The Assault on Hive Lin-Mei is one such conflict, as is the Last March on the Sapphire Worlds. Most acrimonious of all is Operation Chronos, in which a venerated Raven Guard Chaplain fell to Enslaver domination in circumstances where a nearby White Scars force might have been able to intervene. The ill will created by these and numerous other incidents has led to the two Chapters regarding one another with barely contained loathing, a situation that none can see an end to any time soon