From the start of the war, a British blockade on shipments to Germany affected its economy. Germany was particularly dependent on foreign supplies of oil, coal, and grain. Thanks to trade embargoes and the blockade, imports into Germany declined by 80 per cent. To safeguard Swedish iron ore shipments to Germany, Hitler ordered the invasion of Denmark and Norway, which began on 9 April. Denmark fell after less than a day, while most of Norway followed by the end of the month. By early June, Germany occupied all of Norway.