Japan and the Southern Resource Zone

In July–August 1941, after the Japanese occupation of southern French Indochina, the United States, the United Kingdom and the Dutch government in exile freeze Japanese assets and decree an embargo that cuts Japan off from its strategic supplies — first and foremost oil, of which the archipelago imported about 80% from the United States. Rubber falls under the same dependence: nearly 90% comes from British Malaya and the Dutch East Indies.

The decision plays out in imperial and liaison conferences. On 2 July 1941, the Imperial Conference endorses the "advance to the south" even at the risk of war. On 6 September, a new conference sets a deadline: if diplomacy fails to secure the lifting of the embargo by the end of autumn, Japan will prepare for war. The diplomatic path implied a substantial withdrawal from China — a condition set by Washington (the Hull note), judged unacceptable by the army. The military option targeted the "Southern Resource Zone" (Nanpō): oil from Sumatra and Borneo, tin and rubber from Malaya. Freezing its ambitions amounted to letting the oil stocks melt away.

The question put to the imperial government is therefore clear-cut: yield in order to lift the embargo, seize the resources by force, or give up.