For years as technology advanced tensions rose. The boarder between the Changeling Lands and Equestria Militarised, other nations became bigger in terms of their impact of the world and machiens advanced.
Now not only pegisus can fly, not only can earth ponies pull large cargo. But with advance comes war. Weapons are no longer sharpened sticks, replaced with black powder and cannons. No longer are there small skirmishes but entire wars with countless dead.
These are stories told by those who were apart of it, those who fought and sacrificed for their beleifs and all they held dear.
(This is based on the 'Equestria at War' Mod for Hearts of Iron 4 and my time speant with it. If you want to experience some of the fun adventures check it out, its free and worth the time)