 Complete the following phrase:  Although Poland-Lithuania was unaffected by the Thirty Years War 16181648, the following two decades subjected the nation to one of its worst trials ever. This colorful but ruinous interval, the stuff of legend and popular historical novels of Nobel laureate Henryk Sienkiewicz, became known as potop, or the Deluge, for the magnitude and suddenness of its hardships. The emergency began when the Ukrainian Cossacks rose in revolt and declared an independent state based in the vicinity of Kiev, allied with the Crimean Tatars and the Ottoman Empire. Their leader Bohdan Khmelnytsky defeated Polish armies in 