LAURENCE REES: And so why did the Japanese not decide to attack the  Dutch East Indies instead and get the oil that way? Thus leaving America out of the equation.

AKIRA IRIYE: That would be the south-east Asian scenario, so Japan goes to the Dutch East Indies, not even touching British Empire, let alone the United States. What would have happened? I think in pure logic that might have made some sense but whether the United States or British would come to the aid of the Dutch, that’s the question, right? Suppose the Japanese from Indochina decide to penetrate by force the Dutch East Indies. They had been negotiating for oil, because I think throughout the spring [of 1941] they were anticipating some cutback for all shipments from the United States. The Japanese had sent an ambassador to negotiate some kind of arrangement, but throughout 1941 the Dutch authorities had refused to come to any agreement with Japan because the Dutch were under British and American pressure not to accede to Japanese demands.

So the only way the Japanese could have gotten oil from that Dutch East Indies would have been by invading and taking over the oilfields and the refineries; something like that. If that should happen would the United States or the British come to the aid of the Dutch? I think the British would. I think Churchill virtually said that they would come in and reach the Japanese. The only question is would the United States have come in? Churchill asked that question of Roosevelt at the Atlantic Conference in August and Roosevelt is not one hundred percent committing himself. And he says basically that he might do it but he’s not going to commit himself yet.

There is some evidence that as of December 1st Roosevelt finally lets Churchill know that if Japan should attack the Dutch East Indies and the British came to their defence then the United States would come into the war as well. The Japanese had no way of knowing that, but they had assumed that all along, because of what A,B,C,D is saying they could not quite separate A from B or B from the D or so on, so once they got into the Dutch East Indies they would have to be prepared for a war against the United States as well.