The Polish-Lithuanian Commonwealth in 1618 was one of the largest, most populous countries in Europe. It had an elective monarchy and was run by nobility who avoided becoming embroiled in the destructive Thirty Years’ War, which ranged Protestants against Roman Catholics and was beginning to devastate the Holy Roman Empire (1618–48). The Commonwealth was reaching the end of a Golden Age and its decline was partially due to its border wars and expansionist agenda. The Polish-Muscovite War of 1605–18 began with a Polish intervention in the Russian civil war and ended in 1618 with the Truce of Deulino, which permitted Poland to lay claim to Smolensk. A 1617–18 war with Sweden ended in a truce, but no concessions. These wars, far from victories, had an attritional effect, with the depleted Polish-Lithuanian commonwealth further weakened by internal tensions brought about by the rise of nationalist movements on its eastern borders.
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