Union of Lublin creates the Polish-Lithuanian Commonwealth

On July 1, 1569, after months of bitter argument, the joint parliament meeting at Lublin approved the union of the Kingdom of Poland and the Grand Duchy of Lithuania. The two states had shared a king since 1386, when Lithuania's Grand Duke Jogaila took the Polish crown by marriage, but each had its own laws, army and treasury. At Lublin they became one Commonwealth of Both Nations with a single elected king, a common parliament (the Sejm) and a shared foreign policy, while each state kept its own army, treasury and laws.¹

The pressure came from the east. Muscovy under Ivan IV was fighting Lithuania in the Livonian War, and Lithuanian magnates, who feared defeat, were ready to accept help. The Polish gentry wanted the union and the new lands, and the old Jagiellon dynasty was dying out: King Sigismund II Augustus had no children, and he pushed for union before his death in 1572. Lithuanian leaders walked out of the talks, and Sigismund then transferred Lithuania's southern provinces, Podlasie, Volhynia and Kyiv among them, directly to the Polish Crown, and the Lithuanians returned and signed.¹

After 1572, kings were elected by the noble class (szlachta), which formed about 8 percent of the population and held remarkable rights. A 1573 pact, the Warsaw Confederation, promised nobles of all faiths peace with each other, in an age of religious wars elsewhere, so Catholics, Protestants, Orthodox, Jews and Muslims found a place there. The Commonwealth became one of the largest states in Europe, reaching roughly a million square kilometers. Its weak kings and veto-wielding nobles made it hard to govern, and it was carved up by its neighbors from 1772.²