Demon Castle War

These wars are first mentioned in Castlevania: Aria of Sorrow. In the game, you can acquire and equip an actual uniform from the battle. Also, many undead soldiers Soma meets in the castle are those "who marched in their death" some 30 years before (so the Wars occur in 2005).

The course of the war is not explained directly in the game, but most likely it led to Julius Belmont's amnesia and Dracula's true final demise. Whether or not a game will describe the Wars will ever be released has not yet been confirmed.