- what caused the occurence in medieval feudalism in Earth's history (note that before there was Democracy(Greece) and Republic(Rome) then it switched to feudalism (medieval europe) and then is switched to democracy/republic again (modern times))? It was not a linear evolution of the government types (more like a jojo ), it seems something strange/unusual caused it. Maybe the scientific/whatever regress after the fall of the Roman Empire?
The feudal countries like England, France, and Germany didn't go from democracy to feudal. The feudal system arose out the traditional tribal cultures and power bases that expanded to fill to power vacuum left after the fall of the Roman Empire. In fact the city state of Athens went from a system of hereditary rule to one led by tyrants, at that time a tyrant was someone who ruled by popular support rather than divine right, and then on to system of democracy. Also interesting enough wealthy Athenians were required to provide ships in time of war. It’s hard to imagine now a days that if the America went to war that Apple and Google would have to donate an aircraft carrier or two to the war effort but that's would it would be like today under the Athenian system.
I could see a system in the future loosely based on the Shoguns of Japan.
The expansion into space has been taken over by a loose association of power blocs. These power blocs are made up of former nations, organizations, corporations, and wealth families each looking to stake their claim on new frontier with their own vision for it. Power blocs have their own fleets and armies and are responsible for governing their territories while pledging support to the central authority that is earth.
Territories all center around one or more strategic assets they might be a worm hole, a habitable planet, or an asteroid field rich in minerals and extend as far as the power bloc can effectively control. Colonies tend to be small with populations no bigger than an earth city, as such the vast amount of humanity still live on earth and it’s thanks to this and historic allegiance the emperor has effective control. However they have to carefully manage the power blocs and establish their own power base or be reduced to a mere figure head.