"The Unknown Eastern Front: The Wehrmacht and Hitler's Foreign Soldiers" by Rolf-Dieter Muller gives a brief account of the various formations that joined the Wehrmacht or became units (ranging from battalions to divisions) within the German Wehrmacht and Waffen SS. The book is divided into three sections dealing initially with Germany's allies (Finland, Hungary, Romania, Italy, Slovakia, and Croatia), volunteers from neutral and occupied territories (Spain, France, Belgium, The Netherlands, Denmark, and Norway), and Eastern European states (Estonia, Latvia, Lithuania, Poland, Byelorussia, Ukraine, Russia, and the Caucasus). The territory covered here would take two dozen volumes to truly understand. While there are a multitude of works that deal with local collaboration and foreign units in the German Armed Forces throughout the Second World War, the majority rely on presenting just one nation or ethnicity and thus leave out the impact that all of these foreign soldiers had on the German war effort.
Muller deals with numerous complex issues and, more often than not, provides a good foundation for understanding just how complicated and convoluted German policy was when dealing with allies, collaborators, and the local population of whatever territory is being considered and discussed. Unfortunately, because this a slim volume, it barely skims the surface of many issues that need to come to the forefront when studying both the war the Wehrmacht waged on the Eastern Front as well as the Wehrmacht itself. This is a great introduction for those interested in the Second World War and the Eastern Front. You should have some basic knowledge about battles, events, and main characters (both nations and individuals) as while there is some context presented much more is left out. Additionally, there are also numerous weaknesses and errors sprinkled throughout the text, including the idea that Richard Sorge predicted the date the Germans were going to invade the Soviet Union, an ambiguous statement about Stalin's reaction to the invasion, a lack of endnotes for every chapter (often some interesting information is present but no source is listed), and at least in one instance (chapter on Hungary) there are some 30 endnotes in the text but only 17 in the endnote section at the end of the book(!).
For those familiar with the Eastern Front and Germany's efforts, little presented here is original information or groundbreaking analysis. Rather, Muller does something that often escapes many of us who study this subject in-depth. To begin, lets take a step back and look at what made possible Germany's ability to wage war. If we leave the Eastern Front for a moment and take a look at Germany's previous 'miracles' during the initial stages of the Second World War, what do we see? An initial invasion of Poland that received help some two weeks later from a Red Army invasion from the East. A miraculous victory over France that saw Italy join in the war and, unfortunately, much of France's army and air force remain uncommitted for various reasons. Finally, the struggles in North Africa relied heavily on Italian forces and the Italian navy. Yet who gets the credit? Germany. Now, moving on to the Eastern Front. The initial invasion featured some one million foreign volunteers from allied Finland, Romania, Hungary, Slovakia, in addition to tens of thousands of foreigners within the German Army. While German forces advanced on a 2,000-kilometer front, their allies held some 1,200 kilometers of frontline for them, allowing them to concentrate on encirclements at Kiev, Briansk, and Viazma. In 1942, as German forces continued to deteriorate through attrition, further allied forces were mobilized and fielded together with additional foreign volunteers, allowing for the German advance on Stalingrad and the Caucasus. Finally, after the destruction of the German Sixth Army around Stalingrad, it was with the aid of foreign helpers that the Wehrmacht continued to put up a fight for as long as it did. And, of course, not to forget the help that local populations and foreign volunteers offered in the rear-areas that were routinely contested by partisan forces throughout Eastern Europe. Over 3 million allies and volunteers went through the ranks of the Wehrmacht and Waffen SS throughout the Second World War, helping Germany wage a war of genocide (which many foreigners also participated in). For all those who keep wondering how it was possible that Germany could fight for so long against the combined might of the USSR, Britain, and America, this book in part details a very important factor that contributed to German success and is often overlooked.