Correcting the Timeline: US Embargoes on Japan (1940 vs. 1941)

The premise of the question contains a common historical inaccuracy. The United States did not impose a comprehensive embargo on naval and aviation supplies to Japan in 1940. The escalation occurred in two distinct phases during 1941:

July 1940: Export Control Act & "Moral Embargo"

President Roosevelt signed the Export Control Act, allowing restriction of strategic materials. Initially applied to aviation gasoline (87+ octane), high-grade scrap iron/steel, and lubricants—not a total ban on naval/aviation supplies. Japan could still purchase oil, regular gasoline, and many metals.

July 26, 1941: The "Freeze Order" (Executive Order 8832)

Following Japan's occupation of southern French Indochina (July 24, 1941), Roosevelt froze all Japanese assets in the US. This effectively ended all trade, including oil (90% of Japan's supply), scrap metal, and machinery. Britain and the Dutch East Indies followed suit.

Why the Distinction Matters

• The 1940 measures were pressure tactics; Japan still had alternatives.
• The July 1941 freeze was an economic strangulation. Japanese leadership viewed it as an existential threat, directly driving the decision for the Pearl Harbor attack (Dec 7, 1941) to seize Southeast Asian resources.

Thus, the critical embargo was a 1941 response to Indochina, not a 1940 initiative.