The Earth-Mars War was a conflict between sapiens‘ homeworld and its first home away from Earth. Specifically, it was an attempt by the Mars Provisional Authority to breakaway from the United Nations, either becoming a full member in its own right or an independent world.
The conflict did not engulf the outer worlds and asteroids of Sol System but did result in UN crackdowns on Jefivah, Aurora, and Tian. Of all the existing human outposts beyond Sol, only Etrusca remained unaffected. Etrusca, accessible only via the new projection-drive technology and a new invention called a hypergate, declared itself independent of Earth and enforced it by restricting access to the planet. It offered to form a new polity with other human worlds in exchange for Dasarius Interstellar building a hypergate at no charge.
Eventually, Earth and Mars settled the conflict by crafting the original Compact of Humanity in Assembly. Initially a treaty of peace that put most of the existing ten human worlds on equal footing, including Sol’s belts, gas and ice giants, and minor planets as the Jovian Federation. Etrusca joined in exchange for exclusive rights to build a hypergate network. Aurora initially did not sign and remained independent for decades afterward.