Ten years ago, Equestria was nearly destroyed in a combined invasion of its worst enemies. Only with the timely intervention of its erstwhile human allies was the nation spared slavery and extinction. The war is over now, and the treaties of peace faithfully followed even after a decade. While earth ponies help rebuild Earth's ecosystem, human tractors erect roads and cities with terrifying speed.

Sweetie Belle helped make victory possible, but the cost of that victory was one of her best friends. Equestria is safe now, and ponies are spreading to the stars. Why doesn't she feel happier?