This three-volume series will describe and analyses the ‘Swedish Deluge’ (potop szwedski), the devastating 1655–1660 series of wars fought between Sweden, the Polish-Lithuanian Commonwealth, Brandenburg-Prussia, Muscovite Russia, Transylvania, Cossack Ukraine, the Tatar Khanate of Crimea, and the Holy Roman Empire during the reign of Swedish King Charles X Gustavus, an experienced former general from the Thirty Years’ War. By invading the Polish-Lithuanian Commonwealth, King Charles saw an opportunity to put an end to the Polish King’s claim to the Swedish throne and to gain additional territories which would enable him to control the Baltic Sea maritime trade. The book focuses on the Swedish–Commonwealth war, which provoked the political and military collapse of the Commonwealth. However, since this conflict cannot be disentangled from the simultaneous wars between the Commonwealth and Muscovy, from 1654 to 1667, and between Sweden and Muscovy, from 1656 to 1661, they are described as well. Meanwhile, the Ukrainian cossacks fought for freedom from what they perceived as the oppression of the Commonwealth. Michael Fredholm von Essen presents new research on a war previously seldom described in English. Moreover, the book explains the continued development of the Swedish Army after the Thirty Years’ War. It also provides full details on the dissimilar military systems of the Polish-Lithuanian Commonwealth, Brandenburg-Prussia, Muscovite Russia, Cossack Ukraine, Transylvania, the Crimean Tatar Khanate, and the Imperial expeditionary forces engaged in the Swedish Deluge. The wars of the Swedish Deluge were complex in origin and operations and covered a huge territory, from the Arctic north to the shores of the Black Sea. For this reason, the present work is divided into three volumes. Volume 1 describes the armies of the countries at war during the Deluge. Volume 2 will describe the wars in the east, during the period 1655-1657. Volume 3, finally, will describe the Danish wars of 1657-1660 and the conclusion of the wars in the east.