It's been over a thousand years since Equestria saw a serious and prolonged conflict. As of 1009, that is about to change, and by extension, the lives of everypony involved.
The War ended years ago, but some things? They never really leave you be, war or no war. They're the kinds of things that you take, from the present to the grave.
The Equestrian Empire and The United Socialist States of Gryphonia (USSG) Went to war with each other at the beginning of the new millenium, over a border country called Chenarus. Something happened after the war that nopony ever expected...