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).