Mankind had been looking for inhabitable planets for thousands of years since what we call Galaxian Exodus began. It was the year 3,152 in GC (Galaxian calendar) when they found a planet, PXW-A3, and saw hope of survival. At that time they couldn't even imagine that it was indeed the end of Exodus and the beginning of a new galaxian empire of mankind for next 2 thousand years. Luckily, their planet turned out to be exceptionally rich in resource deposit, which became the foundation of the solid advancement of science and military power for empire development.
Discovery of Xion energy and Outbreak of Galaxy War
GC 4,714, a whole new material in a form of powder was found while exploring neighbor galaxies of PXW-A3. Hundreds of years of research finally succeeded in generating energy with unprecedented efficiency from processed Xion crystals. It was then that the course of history was changed. We still remember the ferocity and mercilessness of Nightmare, the first warship of Xion energy when it first appeared in battle-field. Facing Nightmares of Xion, empires had no choice but to form military alliances, which resulted in the Galaxy War I. Afterwards Xion technology drew attention of all the large empires throughout the universe, and struggles for Xion often led to military conflicts and terrible wars.
Proliferation of Wars
Along with the propagation of Xion technology, military conflicts spread exponentially. By the time of the Galaxy War XII, it wasn't very difficult to see all-out wars between large empires and witness a total collapse of civilization. We were hurting each other too much. Rationally, a number of strong empires founded Intergalactic Peace Federation (IPF) and passed the regulations about banning Hyperspace missiles and Carrier-tier warships. IPF won the galaxy-wide support and assumed the role of the peace. guardian. But not for a long time.
There were a number of militant groups of bandits who were notorious for their indiscriminate assaults, destroying ships only to collect debris. In order to defend themselves, empires which couldn't entirely depend on IPF began to build Carrier-Tier War-Ships secretly in their colony planets, violating the regulations. Others followed one by one, sometimes without any obvious need to defend themselves, questioning the effectiveness of IPF regulations. I presume ......