IMO The Man in The High Castle's Events is the definition of Impossible
Well, in the Reddit post, one argues that the Romans, Mongols, and the British did just that.
While I don't think the overall scenario of Man in the High Castle is very realistic, there is historic precedent for relatively small political entities to control vast amounts of territory. Just look at the Roman or the British Empire for example, neither of which were very large at their core.
But remember there was war propaganda at that time that the Nazis and the Japanese were out to gobble the world.
Further reading:
In March 1942, the U.S. was fully engaged in the second World War, fighting against Japan and Germany. The Pearl Harbor attack had happened just months prior, and now there was a U-boat war happening right off the <a href="http://www.learnnc.org/l…
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LIFE magazine's illustrations convey both how Axis powers could've invaded and how plausible Americans thought it was.
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Redcoats raze Washington D.C., Aug. 24, 1814 — the first and last time a foreign army has invaded the continental United States. (Image source: Wikimedia Commons) “Amazingly a number of nations (both friendly and hostile...
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People also feared German or Japanese landings. Especially after Pearl Harbor, there was a concern in the higher-ups that Japanese would seize Hawaii and the West Coast. After all, the Japanese did land in the Aleutian Islands (part of Alaska, which at that time was an
incorporated territory) so technically the United States was invaded. The Japanse also shelled California and Oregon with submarines and fire balloons. One Japanese man is credited with the only bombing on the U.S. mainland in modern warfare.
The bombs Fujita dropped on a forest in Oregon caused little damage. But many years later, Fujita's story became an emblem of reconciliation.
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The far-Northern territories aren’t as large in reality as the map’s projection.
Maps tend to make projections look bigger. Even OTL Russia isn't as big when seen from space compared to how a flat map shows it.