The Green Belt is earned by laddermating. A laddermate is the situation on a chessboard when you compress your opponent's king against the nearest wall and it checkmates them. The principal behind a laddermate is to use two pieces to alternate checking: one holds a file secure while the other checks and moves the opponent's king toward a wall. Check out this series of eight positions on a chessboard. This process of crushing your opponent against a wall is known as the laddermate!

Here is an example:

In the above position, white can begin a laddermate! Below is the first compressing step.

Note that the black king is already doomed, and they know it. One white rook secures the second rank, which is green, and the other rook checks, securing the entire third rank, forcing the black king to the fourth rank. Very soon black will run out of ranks to escape to! The above position is what we call "a mate in six." Below is the rest of the slow strangulation of the black king.

The poor black king has run out of escape squares. Raise your hand and call "Referee!" That Green Belt is yours.