my theory: somewhere a war was going on. celestia was the one fueling it causing many other beings to lose their homes and villiages splitting apart the unity that this republic (i like to think its in the south so i call republic of the south) has known for 156 years. luna is against the whole thing and constantly argues with her sister about it. in the end luna devises a plan to join with the southern republic, and create the eternal night so she can weaken her sister. however celestia already knew about this and prepared. luna got sent away for 1000 years and developed an undeniable hatred for her sister. when she gets envoloped by the elements of harmony she sees many images of the recent years. a peace treaty had been astabalished by celestia as one final honor to her banished sister. the beings of the south had not recovered unfortunatly but had made luna thier lead diety