A 1939 conflict removes several advantages Japan later exploited. It cannot easily support a drive on Singapore from Indochina, while the American battle fleet is still based on the US West Coast rather than at Pearl Harbor. Japanese leaders would have to choose between invading the Philippines before the Allies concentrated or retaining it as the forward edge of an attritional defense. The Philippines therefore become the most consequential possible opening objective because their status shapes the contest for the South China Sea and American participation.
Notable Point · 2:26:50-2:31:12
Why the Philippines becomes Japan's immediate dilemma
Without French Indochina or a Pearl Harbor target, Japanese planners would have to weigh an early move against the Philippines.