1. Archduke Ferdinand is murdered,
causing World War 1.
2. The Allies win WW1, imposing the Treaty
of Versailles on Germany.
3. This causes tension between Germany
and the rest of Europe, something Adolf
Hitler takes advantage of and begins WW2.
4. Japan joins the axis in WW2 in order to
expand their empire.
5. The Axis is defeated, and Japan comes
under US occupation.
6. American soldiers bring comic books,
cartoons, and other American mediums
to Japan which stay behind even after the
occupation is over.
7. Post-WW2 Japan imposes strict
censorship laws that include the banning of
most conventional porn.
8. Japanese citizens retaliate by drawing
comics with women having sex with vaguely
penis-shaped objects like tentacles to
exploit loopholes in the law.
9. It establishes itself as a fetish even after
the laws are relaxed, and so Hentai was born.
Source:
https://old.reddit.com/s3usz6