The United Federation of Planets was an interstellar democratic nation unified after the end of the Earth-Romulan War in 2161. By the end of the 24th century, it included 155 member states and several colonies and protectorates devoted to the principles of democracy, scientific advancement, peace, and equality among along beings regardless of their species or origins. New member states were allowed as long as they honored the Federation’s core values. Its capital city was Paris, Earth.
The Federation was established in 2161 when agents of the Elder Council persuaded the governments of Earth and its allies to form a new democratic state devoted to liberty and justice for all mindkind. Its founding members were Earth, Vulcan, Tellar, Andor, and Alpha Centauri. Over the next few centuries, the Federation spread and became one of the most influential political bodies in the Alpha and Beta quadrants.
Although dedicated to peace, the Federation had several conflicts with other interstellar nations. During the 23th century, its principle enemy was the Klingon Empire, which was based on war and imperialism. The conflict ended when the agents of the Elder Council convinced the Klingon High Council that an alliance with the Federation against greater enemies was in their best interest. This led to the signing of the Khitomer Accords in 2293, creating a new peace between the two states. During the next century, the Federation and the Klingons fought side-by-side against new threats, including the Borg Collective.
Despite Elder Council's best efforts, the alliance between the Federation and the Klingons did not last forever. When Romulus and Remus were destroyed by their star going nova in 2387, the Klingons proceded to invade the Romulan Star Empire. When the Federation objected, the Klingon High Council responded by declaring war on them. Due to the new war, along with rising threats from the Borg and other hostile forces, the Federation became more militaristic and authoritarian. The conflict ended in 2440 when the Federation forced the Klingon High Council into an unconditional surender.
In 2525, the Federation entered a new war with the Covenant, a theocratic military alliance built upon worship of beings that they called the Forerunners. The Covenant declared humans, Vulcans, and other humanoids in the Federation to be blasphemous against their gods. The invasion of the Covenant resulted in the destruction of many of the Federation's member worlds and colonies. The war ended in 2553 when members of the Special Warfare Command destroyed the Covenant's Ark.