Luna

Luna, conventionally known as the Moon, is the only natural satellite of Earth and the first body to be colonized by spacefaring Humanity. First visited in the 20th century and colonized in the 21st, Luna played a key role in Humanity's early expansion throughout the Sol system. "The moon is halfway to anywhere" as one 20th century writer put it, and settlers passed through it on their way to Mars and the Jovians. Following the Human-Covenant War, Luna became the site of the Silver City, the Concord of Reconciliation's Earth embassy.

History
Luna had its first permanent outposts set up in the early 21st century. As the Golden Age of Space Colonization began, a lucrative shipbuilding and orbital infrastructure industry quickly developed on Luna due to its low gravity, lack of atmosphere and proximity to Earth. Much of the orbital infrastructure that enabled a permanent human presence in space as well as travel further out into the system was constructed from Lunar raw materials. Even in the centuries to come, Luna remained a trafficked stopover between Earth, the rest of the Sol system, as well as the extrasolar colonies of the Human Sphere, always retaining a large transitory population in addition to its permanent one.

Society and culture
The Lunar settlement boom of the early 21st century inspired thousands of artists and writers on Earth, giving rise to the Selenist movement which characterized the various creative arts of that era.

Many Lunar colonies are built around the Moon's natural features, most prominently domed-over craters or expansive underground tunnel networks centered on the Moon's natural lava tubes. For much of their early history, these colonies mostly lacked artificial gravity, though most have had gravity plating installed in essential areas since the advent of modern gravitics in the 24th century.

Governance and politics
Early on, Luna was a patchwork of numerous national, transnational, corporate and independent holdings and land claims, even more so than Mars. In the lead-up to the Interplanetary Wars, these Lunar polities often acted as the site of proxy wars for Earth nations and corporate entities. Luna was also the site of many battles between Koslovic revolutionaries, Frieden sympathizers, and miscellaneous homegrown factions. Following a series of kinetic strikes on Earth in early 2163 and the consolidation of the UN, the major rebel strongholds on Luna had been neutralized by the nascent UNSC by end of that year. Though the advent of the UEG somewhat simplified Lunar internal politics, much of the underlying complexity remained.