The Harmonic Unification War (重奏統合争乱, Jūsō Tōgō Sōran) was a conflict that broke out when the Harmonic Divine States collapsed, causing a war between the real world and the Harmonic World. It lasted 31 years, from 1457 to 1488 TE and marked the beginning of the provisional rule over the Divine States (now renamed as Far East) and the History Recreation of both world and japanese history in the territories with the Academies.
In the year 1457 of the Testament Era, the Divine States were in the middle of the recreation of the Nanboku-chō Wars and the Muromachi Period. In the court existed two representatives of the Emperor, and this conflict was the struggles between them. The Emperor of the Divine States controlled the environmental gods using the three types of Divine Tools and by doing so, managed the Earth Pulse running through the Divine States. However, the Emperor's line was unrelated to the government. As they were living gods, they were isolated from all mundane things of this world. Therefore, it was the task of the representatives that had been acknowledged by the Imperial Palace to recreate the role of Emperor in the Testament's history. However, despite reaching a truce with a promise to share power between the North and the South, the Northern Court broke the promise as described by the Testament, starting their rule as a dictator. In 1413, the Southern Court rebelled. The Testament's description showed that in the year 1443, the southern court would assault the imperial balance and pillage the Divine Tools. And until they were taken back in 1457, control over the Earth Pulse was lost. The Harmonic Divine States, lost control of their own Earth Pulse, which had been supporting the Altered Space, and they fell towards the original Divine States. More than half of it completely collapsed and was obliterated, however the remaining portion overwrote and fused with these Divine States, still retaining the weather and other conditions that it had when it was still part of the other countries. Because of this, there are many points where the land of the Harmonic Divine States still exist, these being called the Harmonic Territories.
The other countries who had been living in the Harmonic Divine States before, swarmed into the Divine States all at once, not only escaping from the collapse of their world, but also pinning the blame for the incident onto the Divine States. Battles occurred everywhere during thirty years, postponing History Recreation. This was known as Harmonic Unification War, a face to face hostilities between the Middle Divine States, the Harmonic Divine States and the Remote Divine States, with the latter dwellers integrated into the world countries. Eventually the exhausted Divine States surrendered to the invasion forces and the fights came to an end, with the Divine States renamed as the Far East (極東, Kyokutō). As there was nothing about an invasion of the Japanese territories in the Testament and the Far Easterners were putting up resistance, the world countries did not completely annex the Divine States. It was decided to set up the Academy system, with only students being able to participate in political and military affairs and academies being heavily supported by their respective countries. The trick was that only in the Far East was imposed an age limit of 18 years, forcing a graduation that forbids adults to grasp political power like the "students" in the other countries, heavily handicapping the Far East against their provisional rule and avoiding a coup through military or political means.
Inside the Far East and Catholic believers, this war is still considered a taboo that should be not named or remembered when it's not strictly necessary.