In TE 120, Imperial rule of the Human Galaxy was essentially complete. At that time the Empire consisted of 436 worlds. Of these, 301 were Imperial colonies; 46 were worlds that had joined the Empire voluntarily; 89 had been annexed or conquered.
[Of the original 71 Human worlds in 2153 CE, 16 joined the Empire and 55 were annexed during the Formation Wars. Of the 64 non-Imperial-founded colonies afterward, 30 joined and 34 were annexed.]
The process of home rule was slightly different for each of these classes, and they will be dealt with separately.
This class included the six Nexus Worlds as well as 40 others. These planets were permitted to retain whatever home rule they had enjoyed upon entering the Empire. Gradually most of the near-Terran worlds fell under the shadow of Earth, and their governments became nothing more than standard Imperial Administration, despite their original form.
Annexed planets were, as a rule, placed under military rule for a short time -- the usual period was ninety Terran days. When the Imperial Navy withdrew, an Imperial Governor was assigned. His/her usual job was to restore as much native government as possible, as quickly as possible, without compromising defense. In the course of a generation or so, annexed worlds were indistinguishable from voluntary converts.
Colonies were a constant power struggle between Colonial Regulation (ColReg) and the Bureaucratic Corps (BuCorps). In the long run, BuCorps won nearly every time.
ColReg was responsible, from the very first Imperial colony, for planetary government as well as interplanetary regulation. A Colonial Administrator was appointed by ColReg, with due allowence for the wishes of the colonists. Administrator was a management position, and he/she set up what sub-levels of government were needed.
Colonists trained in bureaucracy usually managed to get positions in the Colonial Administration -- and thus the groundwork was was laid for BuCorps' eventual victory.
When the Colony paid off its original debt -- which could be as quickly as five or ten years -- it lost Colonial status and became officially an Imperial world in good standing. At that point, ColReg's involvement was over, and the Colonial Administration passed under the control of BuCorps.
And then, quickly or slowly, Planetary Administration came to resemble all other Planetary Administrations . . . for Administration was what BuCorps did best. There was an Administrator (or Governor, Supervisor, President, or any of a number of other titles), whose responsibility was to see that all ran smoothly within the context of the Imperial Galaxy. There was an entire hierarchy of Directors, Sub-Directors, Chiefs, Managers, Officers, Associates, Deputy Associates, Assistant Deputy Associates, and all the other trappings of BuCorps.
The truth is, only BuCorps itself knew how individual planets were run. BuCorps administration, Galactic or planetary, was an intricate web that could be strong as steel, choking as quicksand, or tenuous as air -- all at the same time.
One thing was always true, however -- essential services always functioned. Phones worked, food was supplied, and the trains always ran on time.
A few worlds with native intelligent species were made Imperial Protectorates; they were basically off limits to all but exobiologists and exopologists. Usually, an Imperial Navy garrison remained in orbit around the planet to protect the natives from exploitation.
The most notable Imperial Protectorate was Kaa.