East Asia Federation, or Eastasia, is a nation that born out from the united of a fragment Far East Russia district, a new-born Republic of Japan, a newly independent Manchuria Union and Greater Mongolia.
In late 2020s, Japan economy officially crashed, become the first victim directly from the fall of China. As a result, the country felt into chaos & almost reversed back to its imperial era, until the young generation in Japan finally had enough of bullshit come from neo-imperialist old timers & their followers.
With the emperor passed away, a down-to-bottom economy and an aging, dying population, a group of young (around 40 - 50) politicians, with support from progressive forces & radical-enough old figureheads, decided it's time to end the century-long monarchy once and for all, and completely turn into a federation.
Today Eastasia is the technological hub of the whole Solar System & the most aggressive pioneer in term of space exploration.