The Mediterranean Alliance was a political unit located in the Mediterranean region of Earth, founded in the mid-21st century and remained into the 23rd century. One prominent member of the Alliance was Gibraltar.
In the 21st century, the Alliance constructed a massive hydroelectric dam across the Straits of Gibraltar which separated the Atlantic Ocean from the Mediterranean Sea, and lowered the depth of the Med by 60 meters. As well as generating electricity to supply Europe and northern Africa, new fertile farm-land had been freed up. (TOS novelization: Star Trek: The Motion Picture)