European Theater

Blitzkrieg, 1939-1940

Germany invaded Poland on September 1, 1939. Britain and France declared war on September 3 but provided no effective military aid to Poland, which was crushed in five weeks. The Soviet Union, per the secret protocols of the Nazi-Soviet Pact, invaded Poland from the east on September 17. Poland was partitioned.

The German military innovation was Blitzkrieg ("lightning war"): rapid combined-arms offensives using tanks, mechanized infantry, and air support to break through and encircle defending forces. After a quiet winter, Germany conquered Denmark and Norway (April 1940), the Netherlands and Belgium (May 1940), and France (May-June 1940) in stunning rapid campaigns. The French collapse was the greatest shock of the early war. Germany occupied northern France directly; southern France was governed by a collaborationist regime at Vichy under Marshal Pétain.