Operation Barbarossa, the German invasion of the Soviet Union, began the largest and most costly campaign in military history. Its failure was a key turning point of the Second World War. The operation was planned as a Blitzkrieg to win Germany its Lebensraum in the East, and the summer of 1941 is well-known for the German army's unprecedented victories and advances. Yet the German Blitzkrieg depended almost entirely upon the motorised Panzer groups, particularly those of Army Group Centre. Using previously unpublished archival records, David Stahel presents a new history of Germany's summer campaign from the perspective of the two largest and most powerful Panzer groups on the Eastern front. Stahel's research provides a fundamental reassessment of Germany's war against the Soviet Union, highlighting the prodigious internal problems of the vital Panzer forces and revealing that their demise in the earliest phase of the war undermined the whole German invasion.