Beginning immediately after World War One and continuing for more than a decade, the German military and the Soviet Union--despite having been mortal enemies--entered into a secret partnership designed to overturn the order in Europe. Centering on covert economic and military cooperation, their arrangement led to the establishment of a network of military bases and industrial facilities on Soviet soil. Through their alliance, Germany gained the space to rebuild its army. In return, the Soviet Union received vital military, technological and economic assistance. Though Hitler ended their partnership in late 1933, he and Stalin would renew it in 1939. The result was the German - and then Soviet - invasion of Poland. Drawing from twenty archives in five countries, including new collections of declassified Russian documents, Faustian Bargain offers the definitive exploration of a shadowy but fateful alliance that led to the outbreak of the Second World War.