The Earth Alliance is the name of a fictional alliance of the nations of Earth and off-world colonies in the television series Babylon 5. The transition of Earth government from a democratic, elected government to an authoritarian, militaristic one and back to a democracy again is a major theme of the series. It is considered one of the five major galactic diplomatic/military powers (Earth Alliance, Narn Regime, Minbari Federation, Centauri Republic and the Vorlon Empire) in the Babylon 5 pilot episode movie "The Gathering". They have separate seats at the head of the council chambers on the Babylon 5 station. The League of Non-Aligned Worlds sit in the general assembly section. The Vorlons departed from the galaxy along with the Shadows and the last few remaining First Ones, leaving the galaxy to the younger races.
The Earth Alliance is one of the galaxy's major powers, arguably the strongest of the younger races (the other being the Minbari federation) in the Babylon 5 universe. Besides Earth, the Alliance includes 23 colonies; some of the more prominent colonies are on Mars, Orion 7, and Proxima 3. One reason for humanity's rapid settlement of the galaxy is the use of long-range Explorer class starships that can build jumpgates; the jumpgates allow colony ships and supply vessels to easily move from one Earth colony to the next.
EarthForce is the military branch of the Earth Alliance, Earth's governing body in the fictional Babylon 5 universe.
Earthforce was founded as a peacekeeping militia with the majority of its members deployed to control terrorist aggression on the ground. It was initially formed from contingents provided by Earth Alliance member countries and later transitioned to direct individual recruitment.
The Fleet was not formed until after the Earth Alliance purchased Jump technology from the Centauri. The first major action of Earth Force was the war against the Dilgar which ended in victory. Unfortunately, this made the force overconfident and they decided to approach the Minbari despite warnings that doing so would be dangerous. As it happens, the warnings were correct as an inadvertently premature first contact ended violently due to a serious misunderstanding that provoked the Earth-Minbari War in which EarthForce found itself hopelessly outmatched. The war culminated in the climatic Battle of the Line, in which the bulk of EarthForce's remaining forces were annihilated before the Minbari mysteriously surrendered on the brink of absolute victory (or not so mysteriously as it later turned out).