War. War changes ponies.

It has a way of shifting priorities and perspectives. None who survive it emerge unscathed. Especially those who weren't supposed to have survived it at all.

An unscheduled detour to uncover a secret was all that saved Starlight Glimmer from dying in the fiery culmination of The Great War, along with everypony else not fortunate enough to have reserved a spot in one of Equestria's many Stables. But she did survive, and found herself in a world she didn't recognize. A world consumed with hate, violence, and death; even when no longer faced with an external zebra threat. A world she couldn't understand.

So now she seeks the only understanding that she cares about any longer: learning the fate of those she loved. Far to the north, she seeks answers to what became of the Crystal Empire, and the husband she left behind.

While it is not necessary for this story, I don't think, I do encourage reading Legacies if you want to find out how Starlight came to find herself a couple hundred years in her future.