A concentrated strike on Singapore could be presented as Japan honoring its alliance with Germany and Italy rather than opening war against the United States. Japan could then move against Brunei and possibly the Dutch East Indies for oil. This path would deny Washington an immediate casus belli and require Congress and the public to decide whether to fight for powers with which America was not formally allied. It would also force Britain and the Netherlands to reconcile their anti-Japanese sanctions with their already demanding war against Germany and Italy.
Chapter · 54:52-56:55
Singapore and a resource war without attacking America
Attacking British and Dutch possessions could secure oil while forcing the United States to debate entering a war without a direct Japanese attack.