The world is much more inter-connected than it was then. The cost of a war with China is orders of magnitude more than the cost of a war with Germany. In fact, for the first several months of WWII, British and French citizens barely noticed the war.

War with China would be extremely painful, every single item that modern life depends upon apart from food will suddenly become scarce. That acts as a powerful deterrent.

> The world is much more inter-connected than it was then. The cost of a war with China is orders of magnitude more than the cost of a war with Germany.

"economic interdependence prevents wars" was commonly accepted to be true in the 1910s, right up until the outbreak of World War I