The Deluge is the name commonly assigned in the history of Poland and Lithuania to a series of wars in the mid-to-late seventeenth century which leave the Polish-Lithuanian Commonwealth in ruins.In a stricter sense, "The Deluge" refers to the Swedish invasion and occupation of the country from 1655–1660; in a general sense it applies to the series of misfortunes beginning with the Khmelnytskyi Uprising in 1648 and ending as late as 1667.The Commonwealth before the deluge had been territorially the largest state in Europe discounting the fragmented, fractious, and non-government called the Holy Roman Empire.

It had a feared army and a large industrious population giving it a solid claim to status as regional power— and many would argue as a great power as well, for while it did not possess a strong navy to project power over the oceans, as a geohistoric polity, it is a giant amongst the smaller states in the region— only the territorial span of the Ottoman empire or the combined European dominions of Spanish empire rival it in size and population.Before "The Deluge", the Commonwealth had been a Central European power; but during the wars the Commonwealth loses an estimated 1/3 of its population (relatively higher losses than during the Second World War), and its status as a great power.