Germany invades Poland on 01.09.1939
France and UK declare war on Germany in response on 03.09.1939
Soviet Union invades Poland on 17.09.1939 as was planned between Hitler and Stalin.
As you noted China and Japan were already at war.
This means that within two and a half weeks of the “conventional” date all major global powers except for the United States were at war.
The conventional date is the most reasonable date to signify the start of a global war.
But there were also 8 months of “phony war” after that date, where Britain and France had declared on Germany, but weren’t actually shooting (much) yet.
all major global powers except for the United States were at war
Yes, but they were effectively separate wars. The UK and France were not concerned with what Japan was doing (yet…that would come later, and admittedly for separate reasons than America’s even later involvement), and Japan was not concerned about Poland or France.
Germany invades Poland on 01.09.1939
France and UK declare war on Germany in response on 03.09.1939
Soviet Union invades Poland on 17.09.1939 as was planned between Hitler and Stalin.
As you noted China and Japan were already at war.
This means that within two and a half weeks of the “conventional” date all major global powers except for the United States were at war.
The conventional date is the most reasonable date to signify the start of a global war.
But there were also 8 months of “phony war” after that date, where Britain and France had declared on Germany, but weren’t actually shooting (much) yet.
Yes, but they were effectively separate wars. The UK and France were not concerned with what Japan was doing (yet…that would come later, and admittedly for separate reasons than America’s even later involvement), and Japan was not concerned about Poland or France.