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After the Secession Wars, both the SDF and UNSA signed the Charon Accords which ended the war and secured peace. However, the SDF took this opportunity to build up and reform its military and space fleets,intending to finally destroy Earth and its legacy at a later date. The SDF also annexed and occupied many Earth off-world colonies, in direct violation of the Charon Accords. Despite these, SATO and UNSA refused to engage the SDF and enforce the Accords, as they were reluctant to engage yet in another war, one they might not win.
The SDF used this to their advantage, attacking supply convoys intended for Earth and backed pirates to attack and raid outposts. They also began to dispute territorial claims, raising tensions and fear that war may spark again. 18 hours before the Geneva Attack, the SDF openly attacked and raided a UNSA Research Facility on Europa. SCAR Team Seven was sent to investigate, destroy the facility and the prototype F-SPAR weapon to prevent it from falling to SDF hands. The SCARs were succesful, however they were captured and executed as the SDF planted their flag on Europa, informally annexing it. Despite the mission result, STRATCOM refused to set the UNSA fleet on war footing and just made way for the Fleet Day Parade.
6 hours before the attack, Admiral Kotch rallied and gave a speech to his troops, telling them that they will finally eradicate the Earth's influence. This was considered as a declaration of war, but STRATCOM only managed to intercept this rally transmission after the Geneva Attack.
Course of the WarEdit
Invasion of GenevaEdit
As SATO and UNSA were celebrating Fleet Day, a SDF sleeper agent took control of the AATIS guns and reprogrammed them to fire on the parade, quickly destroying many unprepared UNSA warships. This also allowed the SDF fleet to jump in and deploy troops, which began to indiscriminately mass murder civilians and military personnel alike while bombarding the already wrecked city. The UNSA however managed to quickly regroup its forces and launch a counterattack, with the Eclipse and a ground force of SCAR and Marine forces retaking control of the AATIS guns and captured the sleeper agent, forcing the SDF to retreat into low orbit. The remaining UNSA fleet chased and destroyed the fleeing SDF invasion fleet. In a last ditch attempt to destroy the UNSA Navy, the Olympus Mons jumps out of Slipstream Space, and attacks the already depleted UNSA fleet, obliterating 8 destroyers with its F-SPAR. However, the Retribution initiated a tactical collision manuever, damaging both ships to the point where the Olympus Mons is forced to retreat. The UNSA is left with just 2 capital ships in operational condition, the destroyer Tigris and the supercarrier Retribution.
The UNSA achieved its strategic objective in the war which was to delay or hold off the SDF from assaulting Earth and buy time to rebuild its fleet. However, it came at the cost of losing their entire original fleet including Tigris and Retribution, the destruction of Earth's Iron Shield and the death of Admiral Raines, although the fate of the STRATCOM staff is currently unknown. The UNSA did recover many resources and facilities from the SDF, enabling them to rebuild their fleet faster than SDF.
The SDF suffered many losses, with much of their entire military organization in shambles and their economy in ruins. Several SDF High Council members, which lead the entire SDF in both state and military affairs, were assassinated in UNSA's Operation Deep Execute. Admiral Kotch, their foremost admiral as well as many Ace captains and pilots were also killed throughout the war. The majority of the SDF fleet was also decimated, due to a Trojan Horse-style attack by the captured Olympus Mons on the SDF's Orbital Shipyard on Mars, and the others destroyed by tag-team tactical ops from the crews of Tigris and Retribution. The SDF also lost its primary means of ship production, with the destruction of their Orbital Shipyard and the UNSA taking control of most resource gathering facilities in the Solar System. With neither efficient ship production nor resource production in their hands, Mars interplanetary power was severely depleted.
The war ultimately ends in a strategic victory for the UNSA, with the Earth safe from a SDF invasion, the SDF military and naval forces crippled and with most resource-producing facilities in the Solar System under its command enabling it to quickly rebuild its effectively fleet unlike the SDF in the immediate future. Despite this, the SDF achieved a tactical victory over the UNSA by decimating its fleet and defensive capabilities. The true end of the war is currently not known for sure, however the final cutscene in Infinite Warfare as well as the situation at the end of the game seems to imply that the UNSA won over the SDF, or at least achieved a stalemate.