Following the Reformation gains accompanied by religious toleration, the Catholic Church embarked on an ideological counter-offensive and Counter-Reformation claimed many converts from Protestant circles.
The disagreements over and the difficulties with the assimilation of the eastern Ruthenian populations of the Commonwealth had become clearly discernible; an attempt to settle the issue was made in the religious Union of Brest.
John III Sobieski, fighting protracted wars with the Ottoman Empire, revived the Commonwealth's military might once more, in the process helping decisively in 1683 to deliver Vienna from a Turkish onslaught.
The government became ineffective because of large scale internal conflicts (e.g. Lubomirski's Rokosz against John II Casimir and other confederations), corrupted legislative processes (liberum veto) and manipulation by foreign interests.
The city was not captured, but Báthory, with his Chancellor Jan Zamoyski, led the Polish army in a decisive campaign and forced Russia to return territories previously taken, gaining Livonia and Polotsk.
During the reign of Sigismund's son, Władysław IV Vasa, the Cossacks in Ukraine revolted against Poland; wars with Russia and Turkey weakened the country; and szlachta obtained new privileges, mainly exemption from income tax.
Under John Casimir, the Cossacks grew in power and at times were able to defeat the Poles; the Swedes occupied much of Poland, including Warsaw, the capital; and the King, abandoned or betrayed by his subjects, had to seek temporary refuge in Silesia.
John Casimir, a broken, disillusioned man, abdicated the Polish throne on 16 September 1668 amid internal anarchy and strife and returned to France, where he joined the Jesuit order and became a monk.
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 1648 and 1652, and after the Cossacks concluded the Treaty of Pereyaslav with Russia in 1654, Tsar Alexis overran the entire eastern part of the Commonwealth (Ukraine) to Lwów (Lviv).
In exchange for breaking the alliance with Sweden, Frederick William, the ruler of Ducal Prussia, was released from his vassalage and became a de facto independent sovereign, while much of the Polish Protestant nobility went over to the side of the Swedes.
For the Commonwealth there was no big payoff for the Turkish victories and the rescuer of Vienna had to cede territories to Russia in return for promised aid against the Crimean Tatars and Turks.
Beginning in the 17th century, because of the deteriorating state of internal politics and government and destructive wars, the nobles' democracy gradually declined into anarchy, making the once powerful Commonwealth vulnerable to foreign interference and intervention.
The disorganized and increasingly decentralized nature of tax gathering and the numerous exceptions from taxation meant that the king and the state had insufficient revenue to perform military or civilian functions.
Unlike Spain and Sweden, great powers that were allowed to settle peacefully into secondary status at the periphery of Europe at the end of their time of glory, Poland endured its decline at the strategic crossroads of the continent.
During the reign of Peter the Great (1682–1725), the Commonwealth fell under the dominance of Russia, and by the middle of the 18th century Poland-Lithuania had been made a virtual protectorate of its eastern neighbor, retaining only a theoretical right to self-rule.
Several decades before the loss independence, intellectuals began to reconsider the role of the veto and the nature of Polish liberty, arguing that Poland had not been progressing as fast as the rest of Europe because of a lack of political stability.
In the contest for the crown of the Commonwealth he defeated his main rival, François Louis, Prince of Conti, who was supported by France, and King John III's son, Jakub.
In alliance with Peter the Great of Russia, Augustus won back Podolia and western Ukraine and concluded the long series of Polish-Turkish wars by the Treaty of Karlowitz (1699).
Augustus II was helpless when, in 1701, the Elector of Brandenburg proclaimed himself sovereign "King in Prussia," as Frederick I and founded the aggressive, militaristic Prussian state, which would eventually form nucleus of a united Germany.
Augustus III's uninvolved reign facilitated political anarchy and further weakened the Commonwealth, while the neighboring Prussia, Austria and especially Russia were becoming increasingly dominant in its affairs.
Partially confounding expectations that he would be an obedient servant of his former mistress, Stanislaw August encouraged a modernization of his realm's dysfunctional political system and achieved a temporary moratorium on use of the liberum veto in sejm (1764–1766).
Through the Polish nobles that Russia controlled (the Confederation of Radom) and Russian Minister to Warsaw Prince Nicholas Repnin, Catherine forced a sejm constitution (comprehensive legislation), which undid Poniatowski's reforms of 1764.
Emperor Joseph II of the Habsburg monarchy and then Empress Catherine agreed, and in 1772 Russia, Prussia, and Austria forced the terms of partition upon the helpless Commonwealth, under the pretext of quelling anarchy and restoring order.
Moreover, the shock of the annexations made clear the dangers of decay in government institutions, creating a body of opinion favorable to reform along the lines of the European Enlightenment.
[7] Conceived in the liberal spirit of the contemporaneous document in the United States, the constitution recast Poland-Lithuania as a hereditary monarchy and got rid of many of the eccentricities and antiquated features of the old system of government.
The new constitution abolished the individual veto in parliament; provided a separation of powers among the legislative, executive, and judicial branches of government; and established "people's sovereignty" (for the noble and bourgeois classes).
Although never fully implemented, the Constitution of May 3 gained a cherished position in the Polish political heritage; tradition marks the anniversary of its passage as the country's most important civic holiday.
In the wake of the insurrection of 1794, Russia, Prussia, and Austria carried out the third and final partition of Poland-Lithuania in 1795, erasing the Commonwealth of Two Nations from the map and pledging to never allow its return.