In World War 2, Hitler was the leader of Nazi Germany and initiated several military campaigns and alliances. He invaded Poland in 1939, which marked the beginning of the war. Hitler also invaded and occupied several countries in Europe, including France, Belgium, the Netherlands, and Norway. He ordered the extermination of millions of Jews, as well as other groups, in the Holocaust. However, Hitler's aggressive expansion ultimately led to Germany's defeat and his own death in 1945.