At the same time that I am reading Citizen Soldiers, I am also reading an account of Napoleon's invasion of Russia in 1812. One of the marked characteristics of Napoleon's invasion army was its multi-nationality. Conscripts and volunteers were drawn from all over Europe.
Likewise with the Wehrmacht at the height of World War II. From Europe and beyond.
The Wehrmacht in Normandy in June of 1944 was an international army. It had troops from every corner of the vast Soviet empire -- Mongolians, Cossacks, Georgians, Muslims, Chinese -- plus men from the Soviet Union's neighboring countries, men who had been conscripted into the Red Army, then captured by the Germans in 1941 or 1942. There were some Koreans, captured by the Red Army in the 1939 war with Japan. In Normandy in June 1944, the 29th Division captured enemy troops of so many different nationalities that one GI blurted to his company commander, "Captain, just who the hell are we fighting, anyway?"