Following the Lunar rebellion in 2098, the many nations of Earth banded together to keep the Lunar rebels from attaining what they sought, independence from Earth as the Lunar Republic.
While Earth had a vastly superior pool of manpower, troops, and weapons, they had little to no available transports when the war broke out to transport them there in large enough numbers and in proper battle suits to fight on the Lunar surface, while the rebels had a vast amount of missile systems aimed at various nations on Earth due to old national rivalries, as well as the human races only Space Military Fleet, which had been built up years prior to the rebellions outbreak as to help keep the rebellion in the rebels favor, while Earth had only a few armed transport ships.
With no way to get troops to Luna to stop the rebellion and a missile strike out of the option without retaliation, Earth was forced to strike a bargain with Luna and granted independence to approximately half of Luna, while the other half remains in Earth's jurisdiction in return for renewal of Lunar-Earth trade. These terms were agreed to in the Treaty of Lunar City, which is the Lunar capital.
Then in 2137, Earth unleashed its newly constructed Space Fleet on Luna, bombing its war industries and landing troops on the Lunar surface, which conquer more than half of the Lunar Republic within weeks of the invasions start, including the capital of Lunar City, which becomes the military capital of the newly reunited Lunar Colony, which is ruled by the International Council of Earth Nations (ICEN), which represents the major Earthian powers, (the United States, the Eurasian Republic, the Ottoman Republic, the Peoples Republic of Asia, and the Oceanic Federation ), all of which own exactly 1/5 of Earthian occupied Luna.
By 2138 the Lunar Army has been defeated by Earthian invasion forces and the Earthian Space Fleet, while the Lunar Space Fleet has fled Luna with a small colonization force numbering 85,000 people, destined for the farside of Mars to establish a resistance government, to which thousands more will go to in the following years. The small remainder of the Lunar Space Fleet still on Luna is defeated in a battle on June 22nd, 2138, which causes the rest of Luna to fall under the ICEN’s control, allowing Earthian forces to occupy the rest of the planet with minimal resistance by next January in 2139, and a brutal military government is put in place along with a permanent occupation force of 120,000 troops and a large space fleet.
By 2145, tensions between Earthian nations over territory and old issues pushed aside by the Lunar Rebellion resurface, and the ICEN tears apart, with the PR of Asia invading the Eurasian Republic and occupying vast amounts of OTL Russia and after using its Space Fleet to bomb most of the ER to rubble, the “Peoples Republic” of Asia declares victory and annexes the country, causing the Ottoman Republic, the Oceanic Federation, and the United States to sign an alliance targeted at the Peoples Republic of Asia, (which is renamed the Peoples Republic of Eurasia), which causes the Lunar colonies to be divided and teo-thirds going to the Ottoman-Oceanic-American (Republican), Alliance, and 1/3rd going to the PRE,, which begins to secretly fund resistance fighters on Allied Luna, which begins to do the same with rebels in the PRE’s Lunar colony, which increases friction between both sides even more.
War finally beaks out in 2189 when Eurasian troops invade the Oceanic Federation and the Ottoman Republic, but when the first troops cross the border the Republican Alliance launches its space fleet and obliterates the invasion forces as well as landing troops in the PRE and liberating the Eurasian Republic while Republican Alliance troops begin a gruesome campaign to occupy the PRA homeland.