Unique short SF story where aliens being invaded by other aliens, went looking for allies (to help save their galactic empire).
While being chased by the antagonistic aliens, they encountered a barrier surrounding a solar system. They somehow managed to disable it and found a solar system where the third planet from the Sun showed signs of life. When they landed, they were received by a human girl who greeted them. The enemy ship which followed them also landed, but were destroyed by the humans easily.
Upon learning of the aliens request, the humans decided to help the aliens, and moved their entire world to follow the aliens' ship. Too late the aliens realized that these humans were the ancient war mongering race which was sealed up eons ago and they had accidentally released them.
Could someone please help to identify this title for me. Thanks.