American entry turns the Philippines into a logistics threat

American entry forces Japan to address the Philippines after all. If the trigger comes a month into the southern campaigns, the available invasion troops must be drawn from Malaya and the Dutch East Indies. Leaving the islands untouched gives American bombers a base beside Japan's supply routes, command links, and communications through the South China Sea. That geographic threat makes a later Philippine campaign difficult to avoid even though avoiding it had justified the original plan. The trigger may come from Hitler rather than from a deliberate Japanese choice, since a German declaration could lead the United States to declare war on Japan as Germany's ally.