[vacri]

Embargos aren't war, otherwise the West is at war with Russia right now due to it's annexation of Crimea and activities in the Ukraine. And does it really count as Germany at war with the Soviets if there were no German troops involved?

Similarly, if you're counting political events that foment war as being part of that war, then WWII started at least as far back as 1919, when Ferdinand Foch stated that the WWI peace treaty "wasn't a peace, but an armstice for 20 years".

The thing is that Japan's military adventurism in China was a regional affair, conducted between neighbours, whereas Germany attacking Poland brought in countries from all inhabited continents except South America.

[ptaipale]

For me, Japan's large-scale military attack in China in 1937 was more than a "political event".

It's not so clear-cut where policy ends and war starts, and when a war turns into a global war, but I cannot say that September 1, 1939, would clearly be where we draw the line. The fighting in China in 1937 (Battle of Shanghai) was actually bigger in scope than the invasion of Poland in September 1939, and with more casualties. Then the Winter War in Finland exceeded these, with big losses for USSR, and then large-scale war started on the Western front in the Battle of France in 1940 which was even bigger than Winter War in terms of casualties.