For every choice, every flip of a coin or roll of a die, time splits itself to cover every possibility. Usually, when the choice has little impact on the fate of the world, these timelines come back together immediately. When they don't, the paths diverge further and further. Equestria has many of these offshoots, worlds where the Nightmare never ended, where chaos reigns, where a purple princess flies over a kingdom where the bombs never fell.
In one of them, Equestria and the universe that contains it, Ungula, are a small part of an infinite Multiverse. One in every billion thinking souls has a Spark of the vast, roiling expanse that lies between the planes of existence. Should that Spark ignite, that person becomes a planeswalker, able to move between universes through an exertion of magic and willpower.
Two such planeswalkers are Ditzy Doo, pegasus pony, and Pinkie Pie, Bearer of Laughter. Together with the other Element Bearers, they stopped the Elements of Harmony from rampaging out of control and restored balance to their world.
Afterwards, they began to compare notes, sharing their experiences and magical repertoires. In time, Pinkie convinced Ditzy to share one of her most potent spells, a direct manipulation of time itself.
Neither knew that when a pink party planeswalker botches magical time-space manipulation—
AAAAAAAAHHHH!
Make way! Coming through!
...well, that happens.
War. War never changes. The whos, wheres, whys, and hows may be different, but these are just details, window dressing compared to the eternal monster of warfare. Even the most idyllic of worlds can fall to War. Even a land once defined by the magic of friendship can be reduced to cinders by fire and radiation.
War never changes, but warriors do. Some bring security. Some expunge the ghosts of the past. Some seek only to survive. Once in a great while, one might bring a day of sunshine and rainbows to a land that has known only storm clouds for centuries.
And, far more often than you'd think, warriors have no idea what they're doing.
