The Phony War, or in Winston Churchill's words the Twilight War, was a phase of World War II in Europe that began on October 6, 1939 with the end of organized Polish resistance and ended on May 10, 1940, with Nazi-Germany's assault on the Benelux countries. In German the term Sitzkrieg is used for the same period.
The term came into general use because although the great powers of Europe had declared war on one another, neither side had yet committed to launching a significant attack and there was little fighting.
In the center of public interest during the Phony War stood the Winter War following Soviet's assault on Finland on November 30th, 1939. Public opinion, particularly in France and Britain, found it easy to side emotionally with democratic Finland, and demanded from their governments effective actions in support of "the brave Finns" against the larger Bolshevist Soviet Union. As a consequence, the Soviet Union was excluded from the League of Nations, and a proposed Franco-British expedition to northern Scandinavia was much debated. On March 20, after the Winter War had ended, Édouard Daladier resigned as Prime Minister in France, due to his failure to aid Finland's defense.
The open discussions on an Allied expedition to northern Scandinavia, also without consent of the neutral Scandinavian countries, and the Altmark incident on February 16th, when (in the Germans' view) the Royal Navy demonstrated grave disrespect for Norway's neutrality, alarmed the Kriegsmarine and gave strong arguments for a German securing of the Norwegian coast, codenamed Weserübung. The German occupation of Denmark and Norway was commenced on April 9th. The Royal Navy was nearby, and already on April 10th the First Battle of Narvik resulted in two sunk German and two sunk British destroyers. April 15-16th British troops were landed in Norway, but within two weeks most of Norway was in German hands - and the British troops were evacuated from southern Norway.
The debacle of the British campaign in Norway, which actually was an offspring of the never realized plans to aid Finland, forced a debate in the House of Commons during which the British Prime Minister Neville Chamberlain was under constant attack. A vote of confidence in his government was won by 281 to 200, but 41 of Chamberlain's Conservative colleagues had voted against him whilst 60 had abstained. The humiliated Chamberlain found it impossible to continue to lead a Conservative government or form a government of national unity (in Britain called a "national government") around him. On May 10 Chamberlain resigned his premiership whilst retaining his leadership of the Conservative Party. The King, George VI, appointed Winston Churchill, who had been a consistent opponent of Chamberlain's policy of appeasement, as his successor and Churchill formed a new coalition government which included Conservative, Labour and Liberal representatives. Later that same day, German troops marched into Belgium, the Netherlands and Luxemburg. The Phony War was over.
The only major military actions during the Phony War were at sea. Notable events among these were: