This article discusses tanks of the interwar period. World War I established the validity of the tank concept and between the two world wars, many nations needed to have tanks, but only a few had the industrial resources to design and build them. During and after World War I, Britain and France were the intellectual leaders in tank design, with other countries generally following and adopting their designs. This early lead would be gradually lost during the course of the 1930s to the Soviet Union and, to a lesser extent, Nazi Germany.