Political map of the Arctic & the Far North 10 April 1940 (Invasion of Denmark and Norway): Germany had agreed to a partition of Eastern Europe with the Soviet Union (Molotov%E2%80%93Ribbentrop Pact), giving the Soviets leeway to attack Finland in late 1939 (Winter War). While the Allies (Allies of World War II) were contemplating how to respond to this (Franco-British plans for intervention in the Winter War), Germany launched a lightning invasion of Denmark and Norway (Operation Weser%C3%BCbung).  The Allies, who had been preparing to intervene in Norway themselves (Plan R 4), were caught by surprise.