'World War' to me implies conflict involving nations all around the world.
All events point to Dec 11th 1941 as the date the war became truly global.
When Japan attacked China it was not a global war. It was a regional conflict.
When Britain and France declared war on Germany.. even though Canada (representing american continent), India, Australia, New Zealand and the South African territories held by the brits and french entered the war as well, it was not a GLOBAL war as one one side of the world the Chinese were fighting the Japanese alone, and the euros/brit Commonwealth were fighting their war on their own.
When Germany attacked Russia it was still not a global war.. as before, the euro/commonwealth was not fighting any asian opponents.
When Pearl Harbor happened and the US entered the war on Dec 7th, it still was NOT a global war. US was at War only with Japan and no other nation was at war with an Asian power and an euro/commonwealth power at the same time.
Technically, World War 2 started on December 11, 1941 when Germany and Italy declared war on the United States thus linking the Asian war with the Euro/Commonwealth war.
While the Russians did not declare war on Japan until almost the very last month of the war, one cannot consider this the truly global date because Japan was an open ally of Germany and Russia was already at war with Germany.
