Dominaria's past includes many stories, but the most formative of them is the namesake for the set: the Brothers' War. Before the timelines bled and the Multiverse itself was mended. Before the invasion of Phyrexians—the first invasion of Phyrexians—sundered the land. Before the Ice Age that froze the plane. (The end of the Brothers' War is what froze the plane.)
The events that led to repeated destruction and challenges for Dominaria began with egos in conflict and the clash of massive machines of war. These titanic weapons are featured on showcase mech basic lands: full-art mech basic lands showcase locations and the mechanical behemoths that battled there.