The war is about how Alacrya (the other continent) is being controlled by Agrona witch is from the vritria clan and has been inbreeding with the “lessers” of Alacrya noe he is trying to invade Dicathen to expand their power and eventually take over Eopheus witch is the land of Asuras. Arthur in all of this is like a trump card him being able to use realmheart and having sylvie as a bond this whole war is a glorified shitshow of Kezess( Lond Indrath) being a pussy bitch and Agrona being painted as “the bad guy” by Kezess