The Force was an energy field that connected all living things in the galaxy. The power of the Force could be used by individuals who were sensitive to it, a power that was tapped through the midi-chlorians. The Force had many alternate names. The Lasats, for example, used to call it the Ashla, and described it as "the spirit of the galaxy."
Earth's connection to The Force was once vibrant until during the Great Hyperspace War Emperor Vitiate constructed a Sith Temple in Antarctica and there condcuted a ritual with many powerful Sith Lords that made the planets connection to The Force become dormant, it wasn't until 15BBY that The Force awoke on Earth.
The Second Earth's connecton was different as in the abilities of benders were connected with the universe of the spirits, only certain elements could be manipulated such as Earth,Fire,Water and Air
The Third Earth possessed a very slim connection with only a few beings in the entipre world able to use it however it is dubbed as "magic".