The motorized formations received much attention in the world press in the opening years of the war , and were cited as the reason for the success of the German invasions of Poland ( September 1939 ) , Norway ( April 1940 ) , Denmark , Belgium , France and Netherlands ( May 1940 ) , Yugoslavia ( April 1941 ) and the early campaigns in the Soviet Union ( June 1941 ) . The motorized formations received much attention in the world press in the opening years of the war , and were cited as the reason for the success of the German invasions of Poland ( September 1939 ) , Norway and Denmark ( April 1940 ) , Belgium , France and Netherlands ( May 1940 ) , Yugoslavia ( April 1941 ) and the early campaigns in the Soviet Union ( June 1941 ) .