Earth is the primary habitation of humanity, however there are roughly a hundred inhabited and terra-formed worlds besides Earth in a cluster roughly 500 light-years, clockwise along the spiral arm and slightly closer to the galactic centre.
Of the hundred odd worlds over a quarter of them exist in several interstellar alliances which form the core of inhabited space which is about thirty light-years in radius from the Muaciai's first terra-formed world, classically called Pleora, today known as the Ini/Aida system. Due to political expediency and a wish to deter interstellar conflict the aforementioned alliances/unions/empires/federations etc. were formed, listed below, oldest to youngest:
Sairen Empire, Formed 2,995 years ago.
Planets: 7 (Ini, Aida, Gor, Lita, Neulaeun, Korma, Aryana + 1 claimed, formerly inhabited world, Lemona)
Noha Princely Confederacy, Formed 1,400 years ago.
Jionai Union, Formed 700 years ago.
Kohor Federation, Formed 400 years ago.
Planets: 13 + 2 claimed formerly inhabited worlds, and also claims Korma (currently part of the Sairen Empire).
Besides these alliances the remaining 70+ terra-formed worlds (and their 7.6 billion people) which may or may not have multinational governing organisations. Most neutral worlds avoid interstellar politics and merely maintain communications for economic opportunities and to lay claim to colonies without conflict. Almost all wars are between nations on the same planet as interstellar campaigns are prohibitively expensive and terra-forming new worlds is the far cheaper but slower alternative for acquiring resources from the myriad of available planets.
Update 2: The Sairen Empire
With the death of the Mari Republic 700 years ago, no other interstellar organisations survived from the era of the Sairen Empire's birth. This leaves the empire as the single remnant of the Late Settlement period. Their survival is often attributed to their lack of interest in outside affairs and permanent neutrality caused by a political system intentionally designed to make unnecessary declarations of war near impossible.
The Sairen Empire originated on the Sairen home-world Lemona, a planet terra-formed by the progenitors, the Muaciai, who during their 420-year existence created over 20 such worlds. With the collapse of the Muaciai, the planet Lemona and her proto-Sairen inhabitants existed as an unaligned world for 52 years, at which point they were brought under the thumb of the Yarovo Empire who reigned over them for 429 years.
It was in the last 21 years of Yarovo reign when a young woman named Nerin self-immolated before a court in protest of her brother's execution. The event echoed through the Sairen people and inflamed the long smouldering resentment of their status as Yarovo imperial subjects. As domestic terrorism and rebellion ensued for the next two decades, several women would take the name 'Nerin' for anonymity and commit sedition against the Empire, generally acting as rallying cry, nearly all of them would be executed for treason, further radicalising the populace who would put a religious significance to these martyrs, believing them to be reincarnations of a goddess or possessed by the spirits of ancient matriarchs depending on the religion of the observers.
Eventually, the Yarovo Empire left, without apparent cause. The Sairen people took it as a victory, though most outside scholars believe the Yarovo had some unrelated problem that resulted in their abandonment of Lemona. Now, for a rare time in history the world was left alone and independent. The nations of Lemona knew they needed to form an empire if they were to avoid being colonised once again, but who would be the Emperor? How could all these people who spoke different languages, worshipped different gods, and had different political structures co-exist? The last two decades had provided the answer, Nerin. Religious elders sought out a war-orphaned youth and crowned her Nerin, Mother of Nations. She was a figurehead with little actual power, but she was a symbol with which all Sairens could identify with. She would be educated to speak the six most prominent languages, and taught the social graces and political apologia so she could act as the mouthpiece for the coming political order. Additional orphans were gathered into her palace, the girls to be maids and trained as future empresses, the boys to be menservants trained into guards, generals, and ambassadors. And so began the long reign of Nerin up to current day, a monarchy which survived centuries of political revolution, religious reformation, and expansion.
Planets of the Sairen Empire by year of annexation:
Lemona, 2,995 years ago. Abandoned 202 years ago due to the Kohor/Sairen war.
Nation States: N/A
Neulaeun, 2,688 years ago by invasion and then treaty.
Nation States: 90
Ethnic Groups: Sairen: 62%, Neulei 37%, Gorzha: 1%.
Ini, 2,023 years ago by retaliatory invasion, destroying the rival Imika Empire.
Nation States: 341
Ethnic Groups: Imika: 60%, Sairen 38%, Neulei: 2%.
Aida, 1,974 years ago by treaty after Ini's fall.
Nation States: 163
Ethnic Groups: Imika: 94%, Sairen: 5%, Kormi: 1%.
Lita, 1,583 years ago by treaty, ending the Litan and Gorzha Federation
Nation States: 295
Ethnic Groups: Litan: 82%, Gorzha 14%, Sairen 4%.
Gor, 1,540 years ago by treaty following their former partners, Lita.
Nation States: 54
Ethnic Groups: Gorzha: 92%, Litan: 5%, Sairen 3%.
Aryana, 1,334 years ago by terra-formation.
Nation States: 146
Ethnic Groups: Sairen: 99%, Imika: 1%
Korma, 510 years ago by treaty.
Nation States: 59
Ethnic Groups: Kormi: 98%, Sairen 2%.
Sairen Empire Totals:
Nation States: 1,148
Ethnic Groups: Sairen: 43% (Easairen 32%, Nimvasairen 11%), Litan: 25%, Imika: 17%, Gorzha: 9%, Neulei: 4%, Kormi: 2%.
Update 3: The Three Sairen (Easairen, Nimvasairen, Srisairen)
Officially, all citizens of the Empire are Sairen regardless of ethnicity or appearance. The term Sairen is divided into three subcategories:
-Easairen (Water Sairen) are what those living outside of the Empire would see as the typical Sairen, the race whose homeworld is Lemona.
-Nimvasairen (Soul Sairen) are "half-blood" Sairen, generally having maternal Easairen ancestors and paternal ancestors who are Litan, Imika, Gorzha, Neulei, Kormi or others. Nimvasairen are generally counted among the "Sairen" ethnicity as they culturally align with the Easairen. If measured separately, Nimvasairen make up roughly a quarter of the "Sairen" populace and 11% of the empire as a whole.
-Srisairen (Star Sairen) make up the rest of the Empire (Litan, Imika, Gorzha, Neulei, and Kormi). In addition, children of Easairen fathers and Srisairen mothers are considered to be Srisairen, not Nimvasairen as it is a general cultural expectation within the Empire for people to conform with their mother's ethnic customs, regardless of their father's heritage.
Despite official terminology, in practical and demographic discussion, only Easairen and Nimvasairen are referred to as "Sairen."
Below are factoids for each of the imperial peoples, all numbers and percentages are estimates as censuses are illegal within the Empire, instead a combination of birth, wedding, and burial records provides imperial governments a general idea of population dynamics.
Population: 1,082,740,000 (including 276,980,000 Nimvasairen)
Average Lifespan: 357 years
Average Height: 132 cm.
Religions: Ailar (Monotheism) 97%, Ancestor worship 2%, Irreligious 1%.
Phenotype traits: Fair to olive skin; blond, white or brown hair; hooded and almond shaped eyelids; yellow, amber, orange, and red irises; gill flaps on cheeks and neck; small, pointed ears that keep close to the skull; males have abundant body and facial hair. Very diverse in appearance due to a history of being subjugated and a social aversion to endogamy.
Average Lifespan: 190 years
Average Height: 151 cm.
Religions: Litan Animism 74%, Ailar 16%, Irreligious 10%.
Phenotype traits: Orange to red skin; high hairline; red, black, and brown curly to wavy hair; faces resemble Southeast Asians; green, blue, and violet irises; dark melanin spots are common down middle and margins of face as well as down sides and middle of body, in usually symmetrical patterns.
Average Lifespan: 112 years
Average Height: 182 cm.
Religions: Ailar 73%, Imika Pantheism 23%, Irreligious 4%.
Phenotype traits: extremely white skin; straight white, platinum or straw-blond hair; hooded, almond and protruding eyelids; blue or silver irises; sharp canines and incisors; bodies both male and female are covered in fine, silky hairs including their faces and palms; pointed ears; angled features; slender framed.
Average Lifespan: 149 years
Average Height: 196 cm.
Religions: Gorzha Polytheism 80%, Ailar 16%, Irreligious 2%, Litan Animism 2%.
Phenotype traits: Very dark skinned ranging in temperature from coal black to reddish brown and blue-grey; skin is tough, not unlike a pachyderm hide; instead of hair Gorzha have protective keratin spines on their back, face, chest, spines are thicker and more prominent on males with females having flat, smaller spines; eyes may be deep set or prominent and iris have been found in every color but brown is typical; sturdy framed.
Average Lifespan: 273 years
Average Height: 167 cm.
Religions: Ailar 96%, Irreligious 4%.
Phenotype traits: very fair to very dark skinned; hair may be any natural color; ears are pointed, almost crescent shaped and bat-like.
Average Lifespan: 124 years
Average Height: 153 cm.
Religions: Ailar 87%, Irreligious 8%, Shamanism 5%
Phenotype traits: Resemble central Europeans, but only black and dark brown hair is common.