Prior to the attack on Pearl Harbor there was no blockade of Japan. Five months before the Pearl Harbor attack the Dutch, English, and Americans announced an embargo on the sale of oil, steel and scrap metal. An embargo is not an act of war; it is an economic and political tool, enforced primarily through laws, regulations, and diplomatic pressure. Its intent is always to solicit acceptable behavior, which in July 1941 meant for Japan to cease its war actions in Manchuria, China, and Indonesia.  All this before Pearl Harbor.

A naval blockade is an act of war. Naval blockades come in two forms: the embargo of selected items and a complete shutdown of ships with cargo of any type. World War I was enmeshed in the endless slugfest of trench warfare when Britain instituted a complete naval blockade to cut off Germany’s access to food, raw materials, and supplies. The Royal Navy blockaded the North Sea, intercepting ships heading to Germany and occupied countries in Europe. This led to severe food shortages and malnutrition among German civilians. It is estimated that 400,000–750,000 German civilian deaths were due to starvation and disease. The blockade contributed significantly to domestic unrest and the eventual German collapse in 1918. The blockade continued even after the armistice (Nov 11, 1918) until the signing of the Treaty of Versailles (June 28, 1919).

Germany’s unrestricted submarine warfare in WWII was an attempt to blockade England from receiving needed supplies including food. Before the war, 70% of Britain’s food supply was imported. In 1942, as German U-boat attacks during the Battle of the Atlantic reached their peak, imports of meat, sugar, fruit, and cereals were drastically cut. This led to severe rationing. Britain successfully avoided famine through a mix of rationing, domestic production, and American aid which began to increase significantly by late 1942 as the Battle of the Atlantic began to turn in favor of the allies.