In 1939, four European countries were invaded:

• Czechoslovakia: German troops entered Prague on 15 March. Bohemia and Moravia became a German protectorate, and Slovakia a German client state.
• Albania: Italy invaded on 7 April and joined it to the Italian crown.
• Poland: Germany invaded on 1 September, and the Soviet Union from the east on 17 September. Warsaw surrendered on 28 September, and the two powers divided the country.
• Finland: the Soviet Union attacked on 30 November, which began the Winter War.

Britain and France declared war on Germany on 3 September because of the attack on Poland. The Baltic states had to accept Soviet bases that autumn, but the Soviet Union occupied them only in June 1940.