The Cenotaph did more than power the Iron Legion. It also held a small continent and its inhabitants in another dimension. When it was destroyed, it opened the way to this new land. The Staff of Qa-Len powered the portal. All that was left was a catalyst.

On the other side, Discord played a flugelhorn. What could possibly go wrong?

Battalion Wars, and all nations, characters, etc associated with it belongs to Nintendo.
MLP belongs to Hasbro.