On 10 May 1940, Hitler reneged on his promise to respect Dutch neutrality and unleashed a devastating blitzkrieg against the Low Countries. After five days of fighting, the Dutch commander-in-chief surrendered, unable to hold out against the German onslaught and unwilling to accept further destruction of Dutch cities. On the same day, Queen Wilhelmina, who now headed a Dutch Government-in-exile in London, having vetoed a cabinet decision to move to Jakarta because she “could not stand the tropical climate”, announced that the Dutch people in the colonies would fight alongside the Allies, by which she meant they would continue in the struggle against Hitler. What was less clear, at least to the British, was whether the Dutch would be prepared to resist a Japanese invasion of the Netherlands East Indies. While it seemed increasingly likely that the Dutch would resist, they were still playing for time, hoping to forestall an attack with their pledge, which they would give Tokyo on 6 June, to go on selling the Japanese strategic raw materials, including tin, rubber, oil and bauxite, from the East Indies so long as these did not fall into German hands.

The Dutch felt that if the Japanese could not obtain these commodities through negotiation they would be increasingly tempted to take them by force. They knew they could not hope to defend the East Indies on their own. Nor did they have any guarantee that the British or the Americans would come to their aid if the NEI were attacked. Those concerns were not misplaced. “We cannot foresee the time,” the British Chiefs of Staff had concluded in 1937, “when our defence forces will be strong enough to safeguard our territory, trade and vital interests against Germany, Italy and Japan simultaneously.” Nothing had changed since those words were written. On the contrary, the scenario the defence chiefs had considered was now unfolding. On 10 June 1940, less than a week after the mass evacuation of British and French troops from Dunkirk, Italy declared war on Britain and France. With their backs to the wall in Europe and the Middle East, the British would be able to provide few additional resources in the Far East should Japan strike south. The United States was to remain at peace for another eighteen months, until the Japanese strike at Pearl Harbor. Southeast Asia was living on borrowed time.