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Polish–Lithuanian Commonwealth

The Union of Lublin of 1569 established the Polish–Lithuanian Commonwealth, a unified federal state with an elective monarchy, but largely governed by the nobility. The latter coincided with a period of prosperity; the Polish-dominated union thereafter becoming a leading power and a major cultural entity, exercising political control over parts of Central, Eastern, Southeastern and Northern Europe. The Polish–Lithuanian Commonwealth occupied approximately 1 million km (390,000 sq mi) at its peak and was the largest state in Europe. Simultaneously, Poland imposed Polonisation policies in newly acquired territories which were met with resistance from ethnic and religious minorities.

In 1573, Henry de Valois of France, the first elected king, approbated the Henrician Articles which obliged future monarchs to respect the rights of nobles. When he left Poland to become King of France, his successor, Stephen Báthory, led a successful campaign in the Livonian War, granting Poland more lands across the eastern shores of the Baltic Sea. State affairs were then headed by Jan Zamoyski, the Crown Chancellor. Stephen's successor, Sigismund III, defeated a rival Habsburg electoral candidate, Archduke Maximilian III, in the War of the Polish Succession (1587–1588). In 1592, Sigismund succeeded his father and John Vasa, in Sweden. The Polish-Swedish union endured until 1599, when he was deposed by the Swedes.

In 1609, Sigismund invaded Russia which was engulfed in a civil war, and a year later the Polish winged hussar units under Stanisław Żółkiewski occupied Moscow for two years after defeating the Russians at Klushino. Sigismund also countered the Ottoman Empire in the southeast; at Khotyn in 1621 Jan Karol Chodkiewicz achieved a decisive victory against the Turks, which ushered the downfall of Sultan Osman II.

Sigismund's long reign in Poland coincided with the Silver Age. The liberal Władysław IV effectively defended Poland's territorial possessions but after his death the vast Commonwealth began declining from internal disorder and constant warfare. In 1648, the Polish hegemony over Ukraine sparked the Khmelnytsky Uprising, followed by the decimating Swedish Deluge during the Second Northern War, and Prussia's independence in 1657. In 1683, John III Sobieski re-established military prowess when he halted the advance of an Ottoman Army into Europe at the Battle of Vienna. The Saxon era, under Augustus II and Augustus III, saw neighboring powers grow in strength at the expense of Poland. Both Saxon kings faced opposition from Stanisław Leszczyński during the Great Northern War (1700) and the War of the Polish Succession (1733).