Does anybody remember the description I wrote about my custom empire called The Dominion of Man? If not, you can read it here.
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The Dominion of Man is a form of a despotic hegemony which consists of two ruling bodies - Emperor and the Senate. The Senate is made up of 30 senators chosen by the Emperor each specialized in a certain field of science, economy or politics. Whilist the Senate's legislative, executive, and judiciary powers are mostly ceremonial, it does handle most of societal governing. The true power lies with the Emperor and is passed down the dynasty. If the Emperor dies without an heir, the Senate receives emergency powers and fully governs the Empire until a newly elected Emperor. To prevent the Senate from not electing the Emperor they are given a deadline of 1 year by after which, if failed to meet, the Senate is disbanded and new members are chosen by Overwatch. Overwatch is the Empire's paramilitary order specialised in intelligence gathering and covert operations. They're also used as a personal guard for the Emperor and other persons of interest. Overwatch was created by the founders of the Dominion to ensure that the Dominion remains an autocracy and it is led by government officials handpicked by the Emperor.

The Dominion of Man was founded by the United Nations of Man on Earth after the discovery of intelligent alien life, which has, united humanity. The first contact wasn't peaceful though, as humans saw that as a race, they can easily overpower the newly discovered alien life just by sheer numbers. Massive militarization started after first contact and in 3 years, humanity has brought the alien race to near extinction.

130 years from the first contact, the dominion controls a quadrant in their own galaxy, with 27 human colonized planets and 13 conquered alien planets. Anthropocentrism is what keeps humanity united under one banner and one emperor.
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 Main critic point was "whos to stop the Overwatch or the Senate from taking over?". I made a solution. There is nothing to stop those institutions from doing that. It can happen and there is nothing I want to put in the fictional empire that would make that impossible to happen because it would be too unrealistic.