In spite of efforts to prepare the country militarily, the economy could not sustain a lengthy war of attrition. A strategy was developed based on the tactic of Blitzkrieg ("lightning war"), which involved using quick coordinated assaults that avoided enemy strong points. Attacks began with artillery bombardment, followed by bombing and strafing runs. Next the tanks would attack and finally the infantry would move in to secure the captured area. Victories continued through mid-1940, but the failure to defeat Britain was the first major turning point in the war. The decision to attack the Soviet Union and the decisive defeat at Stalingrad led to the retreat of the German armies and the eventual loss of the war. The total number of soldiers who served in the Wehrmacht from 1935 to 1945 was around 18.2 million, of whom 5.3 million died.
Heinrich Himmler's Schutzstaffel (SS) took full control of the police and the concentration camps throughout Germany in 1934–35. Himmler expanded the role of the camps to hold so-called "racially undesirable elements", such as Jews, Gypsies/Romanis/Sintis, Serbs, Poles, disabled people, and criminals. The number of people in the camps, which had fallen to 7,500, grew again to 21,000 by the start of World War II and peaked at 715,000 in January 1945.