When I was a kid, I learned that World War 2 started in Sept 1939, after the invasion of Poland, and it used to piss me off when I heard Americans say it started after Pearl Harbor in 1941.
Then as I learned more, I realised that thinking it started in Sept 1939 was a Eurocentric point of view, and it could be argued it started with the Second Sino-Japanese war in July 1937, or the invasion of Abyssinia in 1935, or of Manchuria in 1931.
Anyway, not sure why I'm thinking about this now.