An alliance of Earth, Vulcan, Andoria and Tellar formed in the 2150s, the direct predecessor of the United Federation of Planets.
The Coalition of Planets grew out of the cooperation among Earth, Vulcan, Andoria and Tellar in the final season of Enterprise. After the Romulans tried to provoke war between the Andorians and the Tellarites in 2154, Jonathan Archer pressed the rival worlds toward a lasting partnership.
Talks to form the coalition were held on Earth in 2155, when the extremist group Terra Prime threatened them in the episodes Demons and Terra Prime. Archer's appeal for unity helped keep the talks alive, and the alliance became the foundation of the Federation in 2161.