The Empire of Man was formed after the Three-Hundred Year War, when a small think tank decided that a strong central power was needed to prevent more bloodshed.
Empress oversees everything. UEEF is Military Arm, everything else is divided into "Offices" (E.G. Office of Internal Security, Office of Public Health)
keep the peace between the various human worlds
metal from asteroids, the UEEF (Troops, equipment, UEEF Space Corps, etc), Office of Internal Security
After the three nuclear wars (which destroyed Earth, and colonies on the moon and Mars, respectively), Mankind was plunged into a three hundred year war, with Io, Ganymede, and Europa on one side, and Ceres, Enceladus, and Haumea on the other. Eventually, an unnamed think tank realized that the war was going to continue, and likely wipe out Mankind unless a strong central government could unite the warring planets.