From Bulbapedia, the community-driven Pokémon encyclopedia.
The Dragon Force (Japanese: 竜脈 Dragon Pulse) is an important element in White—Victini and Zekrom and Black—Victini and Reshiram.
The Dragon Force is a powerful and invisible energy that surges throughout the Pokémon World. If used wisely, the Dragon Force can be used to create an environment where humans and Pokémon alike can live in harmony. If used wrongly, the Dragon Force can become a destructive and violent energy that threatens to destroy the planet and all that live on it. It was controlled by the Sword of the Vale in the past before being used as a seal on the corrupted energy.
The corrupted Dragon Force
The Dragon Force is introduced in a storybook read by Mannes. He explains how the Dragon Force was used by the People of the Vale to cultivate their land and bring the people and Pokémon together in peace and prosperity. However, the twin sons of the King of the People of the Vale began fighting and started a war. Once the war was over, the two brothers were too late to realize that their fighting caused the Dragon Force to go wild and it began destroying everything.
Seeing the destruction the Dragon Force caused, the King used the power of Victini to move the Sword of the Vale to the location that would eventually become Eindoak Town. This managed to calm the Dragon Force down, but the King died from exhaustion soon after and accidentally left Victini trapped inside of the Sword of the Vale's barrier.
Years later, Damon, in his attempt to restore the land his people once lived in, took control of the Sword of the Vale and attempted to move it back to its previous location. With the plug keeping the Dragon Force in control taken out, it began to go wild once more. Regretting his actions, Damon, with the help of Ash Ketchum and Victini, manages to stop the Dragon Force by absorbing it into the Sword of the Vale and then redirecting its power into space.