From Bulbapedia, the community-driven Pokémon encyclopedia.
Kingdom of the Vale (Japanese: 大地の王国 Kingdom of the Earth) is an anime-exclusive location mentioned in the fourteenth movie. It was once the home of the "People of the Vale." The Kingdom of the Vale was once ruled by a beloved king who had twin sons. The two sons became known as the Hero of Ideals, and the Hero of Truth. Each prince raised great dragon Pokémon; the Hero of Ideals had Zekrom, and the Hero of Truth had Reshiram. One day, a fight broke out between the two princes, and they became mortal enemies. Their anger erupted into a massive war which angered the Dragon Force which supplied the Kingdom with power. With the Dragon Force in turmoil, the king asked his good friend Victini to help him move the Sword of the Vale so that it could calm the rage of the Dragon Force. He gathered the People of the Vale on top of the castle and successfully moved the sword to a new location. With his task completed, the king passed away, telling Victini that should the Sword of the Vale be moved again, it will unleash the rage of the Dragon Force. Overcome with remorse for their actions, the two princes hid the Dark Stone and Light Stone beneath the castle.
In the present, it is Damon's goal to revive the Kingdom of the Vale by once again using the Dragon Force.