There are multiple sentient races in the Milky Way galaxy. Of those, only three are currently known: Humans, Guardians, and Thargoids.
Humans are the most well known race with a robust physiology. They are bipedal mammals and generally strong, fast and agile. They reach physical maturity at around 18 years old. Then they enter the workforce or continue their education for a profession. The average human lifespan is naturally about 79 years, but advanced biotechnology and cybernetics has substantially increased human lifespans. Humans primarily reside in a colonized region colloquially known as "the Bubble", which contains about 19,000 star systems. They originated from the single-star system Sol and the terrestrial planet Earth in the Orion-Cygnus Arm of the Milky Way.
As it has been throughout recorded history, mankind is not very prone to agreement over ethical, political, religious, and economic views. It remains this way today in the 34th Century, with the realm of human-colonized space held by numerous groups under various ideals, some benevolent and others not quite as much.
There are three major factions known as galactic superpowers and several Powers in human-colonized space. The Federation is based in Sol and is a representative-electing democracy. The Empire is based from the system of Achenar and is a hereditary monarchy. The Alliance is based from the system of Alioth and is a confederation of independent systems working cooperatively. Powers are powerful individuals or organizations who strive to control inhabited space for their own agendas in Powerplay. Each Power can control a vast amount of systems that is aligned to both major and minor factions. In addition to the three galactic superpowers and the powers, there are also many minor factions. The faction with the highest influence within the system will usually be the controlling faction of that system. System control falls on the faction that owns the controlling station. The government of a system is ruled by a controlling faction and if that faction is an anarchy no laws will apply in the system.
The Guardians are an alien race thought to be extinct. Their ruins were first discovered in the Synuefe XR-H D11-102 system on October 27, 3302 by CMDR XDeath. They used artificial intelligence, neural implants and the monolith network as the heart of the Guardians' society. The monolith network was used for practically all of their society's communication. The formal basis for the Guardians' communication behaviors was visual rather than verbal, a distinction that arose very early in their development. The Guardians' written language consisted of glyphs that evolved from a form of sign language that the Guardians developed while hunting to communicate stealthily.
The Thargoids are an insectoid alien race who are said to originate outside of known space, perhaps existing in a parallel universe or spacial dimension. They are very hostile and aggressive and have not been interested in diplomatic relations to date. Not much information has been obtained about Thargoid society or culture. The only known fact is that the society is hive based, with no sense of close family. It is thought that the society is divided into colonies, possibly along the lines of ant colonies. On January 5, 3303, Commander DP Sayre reported the first known encounter with an Unknown Ship; these ships are believed to be related to Thargoids, but no connection has been confirmed yet.