Political map of East Asia and the Western Pacific 06 December 1941 (Eve of Pearl Harbor): Germany invaded the Soviet Union in June (Operation Barbarossa), but Japan declined to join her ally, resolving instead to occupy the rest of French Indochina (Japanese invasion of French Indochina). The United States and Britain responded by freezing Japanese assets and stopping oil exports (Events leading to the attack on Pearl Harbor). Without oil, Japan faced the choice of either withdrawing from China (Hull note) or invading the oil-rich East Indies and further provoking the US. By December, Japan had made its decision, mobilizing its fleet for a surprise strike on the US navy (Attack on Pearl Harbor).