expanded Polish power. Major enemies at this time were the German Teutonic Knights and the Tatars. After a period of political unrest Wladyslaw I reunited the kingdom in 1320, and his son Casimir III the Great protected it from its enemies and developed its economy and society. In 1386 Queen Jadwiga married Wladyslaw II Jagiello, the grand duke of Lithuania, uniting two powerful states. In 1410 their armies defeated the German Teutonic Knights at the battle of Tannenberg. In the 16th century, Poland and Lithuania expanded eastward to annex much of the Ukraine and some Russian territory. From this time the Russians also became one of Poland's major opponents. The greatest king of this period was Sigismund II Augustus. In 1572 Sigismund II died without an heir. Under the following Vasa Dynasty, Poland became involved in wars with Sweden, Russia, and Turkey. In 1610 the Poles succeeded in occupying Moscow, but this success was short-lived. Russian advances on Polish territory and a Swedish invasion in 1655 created a major crisis. The Poles fo
...