Added species links
The perks of membership included free trade and movement between the whole of SolGov territory, humanitarian aid to developing stations and colonies, as well as any that suffered a disaster, and eventually military protection from the criminal element that eventually followed Humanity into space. Members could enforce laws within their own borders, provided they followed the Declaration of Rights, and periodically allow observers to examine their societies for compliance.
As colonization continued in bordering systems, and time passed, and humanity continued to stretch out into the stars. SolGov shepherded the peoples of Earth, continuing and creating treaties with the Skrell, making the first contact with the Unathi, and defending humanity from the Vox. Gateways and Bluespace drives allow Humans to spread further and faster than ever before. As humanity develops, so does SolGov, while recently corporations have outpaced the spread of SolGov's influence, SolGov is still highly influential in the more developed systems, and sometimes extends its light as far as the frontier, much to the annoyance of the TSCs.
When Humanity first started colonizing the Solar System, it was under the banner of the Old Earth, nation-states like China, America, and India planted their flags in the dirt of planets and moons throughout the system. Shortly behind them the private corporations followed, establishing corporate outposts and research stations away from the prying eyes of Earth. As the situation on Earth deteriorated, the colonies funded by corporations grew more powerful in the absence of oversight, and the colonies that eventually lost contact with their parent nation-states were left on their own. While some withered, being forced to fend for themselves, and others disappeared entirely, the strongest banded together and started to form some of the settlements and governments that we know so well today. As the flow of people from Earth grew, so did the settlements that had survived.