Army of the Polish-Lithuanian Commonwealth

The military of the Polish–Lithuanian Commonwealth evolved from the merger of the armies of the Kingdom of Poland and the Grand Duchy of Lithuania following the 1569 Union of Lublin, which formed the Polish–Lithuanian Commonwealth. The army was commanded by the Hetmans of the Polish–Lithuanian Commonwealth. The most unique formation of the army was the heavy cavalry in the form of the Polish winged hussars. The Polish–Lithuanian Commonwealth Navy never played a major role in the military structure, and ceased to exist in the mid-17th century.

Commonwealth forces were engaged in numerous conflicts in the south (against the Ottoman Empire), the east (against the Tsardom of Muscovy and later, the Russian Empire) and the north (the Kingdom of Sweden); as well as internal conflicts (most notably, numerous Cossack uprisings). For the first century or so, the Commonwealth military was usually successful, but became less so from around the mid-17th century. Plagued by insufficient funds, it found itself increasingly hard-pressed to defend the country, and inferior in numbers to the growing armies of the Commonwealth's neighbors.

Following the end of the Commonwealth, the Polish military tradition would be continued by Napoleonic Polish Legions and the Army of the Duchy of Warsaw.

The Commonwealth was formed at the Union of Lublin of 1569 from the Kingdom of Poland and the Grand Duchy of Lithuania. The armies of those states differed from the organization common in the west of Europe, as according to Bardach, the mercenary formations (Polish: wojsko najemne), common there, never gained popularity in Poland. Brzezinski, however, notes that foreign mercenaries did form a significant portion of the more elite infantry units, at least till the early 17th century. In the 15th century Poland, several other formations formed the core of the military. There was a small standing army, obrona potoczna ("continuous defense") about 1,500–3,000 strong, paid for by the king, and primarily stationed at the troubled south and eastern borders. It was supplemented by two formations mobilized in case of war: the pospolite ruszenie (Polish levée en masse – feudal levy of mostly noble knights-landholders), and the wojsko zaciężne, recruited by the Polish commanders for the conflict (it differed from Western mercenary formations in that it was commanded by Polish officers, and dissolved after the conflict has ended).

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