The Union of Lublin of 1569 established the Polish–Lithuanian Commonwealth, a federal state more closely unified than the earlier political arrangement between Poland and Lithuania. Poland–Lithuania became an elective monarchy, in which the king was elected by the hereditary nobility. The formal rule of the nobility, who were proportionally more numerous than in other European countries, constituted an early democratic system ("a sophisticated noble democracy"), in contrast to the absolute monarchies prevalent at that time in the rest of Europe.

The beginning of the Commonwealth coincided with a period in Polish history when great political power was attained and advancements in civilization and prosperity took place. The Polish–Lithuanian Union became an influential participant in European affairs and a vital cultural entity that spread Western culture (with Polish characteristics) eastward. In the second half of the 16th century and the first half of the 17th century, the Commonwealth was one of the largest and most populous states in contemporary Europe, with an area approaching one million square kilometres and a population of about ten million. Its economy was dominated by export-focused agriculture. Nationwide religious toleration was guaranteed at the Warsaw Confederation in 1573.