They should have just moved into the Dutch East Indies after the fall of the Netherlands, just as they moved into Indo-China after the fall of France. If they wanted to be more cautious, they could have skipped Indo-China, the East Indies were more important. If they had done this in mid 1940, I seriously doubt the US would have done anything. After all, 1940 was an election year and the isolationists were still very influential.
Good point. The Dutch KNIL was rather weak and could not have held out for long. The Dutch asiatic fleet had nothing heavier than cruisers. Not sure what would have happened to the ABDA command without the Americans. The US had fleets, but not much of an army at that time. As for the Japanese, well, leaving a rather large US “colony” - the Philippines - behind their back probably seemed very risky and dangerous to the Imperial Army planners. You are right to ask “What would the Americans have done?” absent a direct attack from the Japanese. Instead, they rolled the dice and lost big time.Did the league say they could invade the rest of the country? If so, why did Japan walk out of the League after being censured by the Lytton Report?