May 2032, Earth. As global tensions rise WW3 starts, with many different sides and countries fighting each other. NATO and the USA claim most of Africa and northwest Asia, however, the Japanese soon rise against them. Using their overwhelmingly high technology, they take control of most of east Asia and south Australia.
November 2034, two clear sides have formed, NATO, and The New Japanese Empire. But on Nov 20th 2034, The New Japanese Empire revealed weapons far beyond human invention. In reality WW3 was a civil war, with sponsors from Proxima Centauri A and B. In December of 2034 The New Japanese Empire attacked US and UK internet satellites to disturb radio communications. All this did was create a surge of new army recruits. Unfortunately for NATO, The New Japanese Empire still prevailed with faster technology and battle victories. In this win, they assumed power of the entire planet. They used this new power to repaint their enemies as horrible monsters to the public.
Examples
The norse were considered drunks and barbarians
Central European's worst crimes such as WW2 and The French revolutions were taught as horrible european scum acts
The British were displayed as lazy slobs who had tea parties all day and had no respect for those below them
Canadians were shown as wimps, always apologizing for every thing
And the worst, Americans, were shown as greedy, fat, capatilst scum who legalized murder everywhere with free gun laws. Japanese children were taught that they were the worst of all NATO, and betrayed humanity by opposing Japan.