In my world, there are humans (often called Earthlings) and eight alien species.
Humans have an Earth government best described as a democratic quinquevirate: to be exact, this is an elective semi-presidential republic with five Presidents, ten Prime Ministers, and one honorary Emperor/Empress/Empross (this is a United Nations pastiche) (in real life, the United Nations is composed of five permanent members of the Security Council, ten elected members, and a General Secretary).
The eight alien species are (they are provisionary names):
- Blue Squirrels. They look like bear-sized blue-furred squirrels. They live in a matriarchal tribal society. Their cradle is a temperate rainforest planet.
- Mountain Albatrosses. They look like raven-sized red-feathered albatrosses. They live in a theocracy, and individuals of power are celibate priests and celibate priestesses. Their cradle is a mountain planet.
- Huge Forest Tortoises. They look like ostrich-sized green-scaled tortoises. They live in a hereditary semi-presidential republic (both the President and the Prime Minister inherit their respective position from their respective parents, and have limited power). Their cradle is a dry tropical forest planet.
- Orange Desert Flatworms. They look like falcon-sized orange planarians. They live in an elective constitutional monarchy. Their cradle is a sand desert planet.
- Giant Purple Iguanas. They look like gharial-sized purple-scaled iguanas. They live in a Singapore-like benevolent dictatorship. Their cradle is a swamp planet.
- Ice Termites. They look like rabbit-sized yellow termites. They are eusocial and they live in a matriarchal absolute monarchy. Their cradle is an ice planet.
- Sponges. They look like human-sized red sea sponges. They live in a semi-presidential republic with one President and four Prime Ministers. Their cradle is an oceanic planet.
- Purple Cannabises. They look like human-sized purple cannabises. They are best described as benevolent libertarians (if we compare them to humans). Their cradle is a grassland planet.
So, I wonder why would most aliens species have a non-democratic political system.