stylistic:tone, information:extraction
Deluge, rebellions and Vienna (1648–1696)

The Commonwealth's power and stability began waning after a series of blows during the following decades. Władysław's brother, John II Casimir, proved to be weak and impotent. The multicultural and mega-diverse federation already suffered domestic problems. As persecution of religious and ethnic minorities strengthened, several groups started to rebel.

A major rebellion of self-governed Ukrainian Cossacks inhabiting south-eastern borderlands of the Commonwealth rioted against Polish and Catholic oppression of Orthodox Ukraine in 1648, in what came to be known as the Khmelnytsky Uprising. It resulted in a Ukrainian request, under the terms of the Treaty of Pereyaslav, for protection by the Russian Tsar. In 1651, in the face of a growing threat from Poland, and forsaken by his Tatar allies, Khmelnytsky asked the Tsar to incorporate Ukraine as an autonomous duchy under Russian protection. Russian annexation of Zaporizhian Ukraine gradually supplanted Polish influence in that part of Europe. In the years following, Polish settlers, nobles, Catholics and Jews became the victims of retaliation massacres instigated by the Cossacks in their dominions.

The other blow to the Commonwealth was a Swedish invasion in 1655, known as the Deluge, which was supported by troops of Transylvanian Duke George II Rákóczi and Frederick William, Elector of Brandenburg. Under the Treaty of Bromberg in 1657, Catholic Poland was forced to renounce its suzerainty over Protestant Prussia; in 1701 the once-insignificant duchy was transformed into the Kingdom of Prussia, which became a major European power in the 18th century and proved to be Poland's most enduring foe.

In the late 17th century, the king of the weakened Commonwealth, John III Sobieski, allied with Holy Roman Emperor Leopold I to deal crushing defeats to the Ottoman Empire. In 1683, the Battle of Vienna marked the final turning point in the 250-year struggle between the forces of Christian Europe and the Islamic Ottomans. For its centuries-long opposition to Muslim advances, the Commonwealth would gain the name of Antemurale Christianitatis (bulwark of Christianity). During the next 16 years, the Great Turkish War would drive the Turks permanently south of the Danube River, never again to threaten central Europe.