With the signing of the Nazi-Soviet Pact (1939) Hitler had secured a guarantee of non-intereference as he and Stalin secretly divided much of eastern Europe between themselves. Germany could then turn its sights on Western Europe without fearing Soviet intervention.
In April 1940, the Germans invaded Denmark and Norway. A month later, on May 10, 1940, they launched an invasion of Holland, Belgium, Luxembourg and France. Jews from each of those countries and German Jews who had sought refuge there -- such as the family of Anne Frank who had come from to Amsterdam in 1933 – were now trapped by the Nazis and subject to severe anti-Semitic restrictions.
Soon, the Nazis then began the systematic capture and deportation of all Jews to ghettos, transit camps and ultimately to death camps.