The death of Casimir was followed by the temporary separation of Poland Lithuania, and by a strong aristocratic reaction in Poland itself. Casimir's third son, John Albert, was elected king of Poland, and his fourth son, Alexander, became grand-duke of Lithuania. On the death of John Albert in i5o1, Alexander suc ceeded him as king, and the union of Poland and Lithuania assumed a more definite character, the senate of each country agreeing that in future the king of Poland should always be grand duke of Lithuania. The acquiescence of Lithuania was due essen tially to a new danger which had arisen in the East. Till the accession of Ivan III. in 1462 Muscovy had been a negligible factor in Polish politics. During the earlier part of the 15th cen tury the Lithuanian princes had successfully contested Muscovite influence even in Pskov and Great Novgorod. Many Russian historians even maintain that, but for the fact that Witowt had simultaneously to cope with the Teutonic Order and the Tatars, he would have extinguished struggling Muscovy altogether. But since the death of Witowt (143o) the military efficiency of Lithu ania had sensibly declined ; and the natural attraction of the Ortho dox-Greek element in Lithuania towards Muscovy threatened the integrity of the grand-duchy. During the reign of Alexander, who was too poor to maintain any adequate standing army in Lithuania, the Muscovites and Tatars ravaged the whole country at will, and were prevented from conquering it altogether only by their inability to capture the chief fortresses. In Poland, mean while, Alexander had practically surrendered his authority to an incapable aristocracy, while the dependent States of Prussia in the north and Moldavia in the south made strenuous efforts to break away. Fortunately for the integrity of the Polish State the premature death of Alexander in i5o6 brought upon the throne his capable brother Sigismund, the fifth son of Casimir IV. Eminently practical, Sigismund recognized that the first need of Poland was a standing army, that Poland, in order to hold her own, must in future follow the example of the West, and wage her warfare with trained mercenaries. The wide financial and military liberties of the Polish aristocracy for long prevented both the organization of an adequate national army and the develop ment of a modern fiscal system. Much of the internal history of Sigismund's reign turns on the various proposals made towards these ends, most of which were defeated or mutilated by the aristocratic opposition in the diet. The long, open frontiers of the Polish kingdom invited invasion, and the misfortunes which fell on Poland at a later time are largely due to the failure of the defensive measures proposed by Sigismund and his advisers. Throughout his reign, the king was hampered by lack of resources. In 1525 he was compelled to grant autonomy to the province of Prussia instead of annexing it he was unable to succour his unfortunate nephew, Louis of Hungary, against the Turkish peril, or to prevent the occupation of one Lithuanian province after the other by the Muscovites.
The Cossacks.—To this period belong the first attempts to provide for the defence of the dzikie pole, or "savage steppe," as the vast plain was called which extended from Kiev to the Black sea. Thus, in the reign of Alexander, the fugitive serfs who had escaped into this wilderness (they were subsequently known as Kazaki, or Cossacks, a Tatar word meaning freebooters) were formed into companies (c. 1504) and placed at the disposal of the frontier starostas, or lord marchers, of Kaniev, Kamenets, Czerkask on the Don and other places. But these measures proved
inadequate, and in 1533 the lord marcher, Ostafi Daszkiewicz, the hero of Kaniev, which he had successfully defended against a countless host of Turks and Tatars, was consulted by the diet as to the best way of defending the Ukraine permanently against such inroads. The veteran expert advised the populating and fortifying of the islands of the Dnieper. But nothing was done officially. The selfish prudence of Queen Bona did more for the national defence than the Polish State could do. To defend her immense possessions in Volhynia and Podolia, she converted the castles of Bar and Krzemieniec into first-class fortresses, and placed the former in the hands of her Silesian steward, who ac quitted himself so manfully of his charge that "the Tatars fell away from the frontier all the days of Pan Pretficz," and a large population settled securely beneath the walls of Bar, henceforth known as "the bastion of Podolia." The most important political event in eastern Europe during the reign of Sigismund was the collapse of the ancient Hungarian monarchy at Mohacs in 1526. After the death of King Louis in the battle, the emperor Ferdinand and John Zapolya, voivode of Transylvania, competed for the vacant crown, and both were elected almost simultaneously. In Poland Zapolya's was the pop ular cause, and he also found powerful support in the influential and highly gifted Laski family, represented by the Polish chan cellor and his nephews John and Hieronymus. Sigismund, on the other hand, favoured Ferdinand of Austria. He argued that the best way to keep the Turk from Poland was for Austria to incor porate Hungary, in which case the Austrian dominion would be a strong and permanent barrier against a Muslim invasion of Europe. History has more than justified him, and the long duel which ensued between Ferdinand and Zapolya (see HUNGARY : History) enabled the Polish monarch to maintain to the end a cautious but observant neutrality. More than once, indeed, Sigis mund was seriously compromised by the diplomatic vagaries of Hieronymus Laski, who entered the service of Zapolya (since 1529 the protégé of the sultan), and greatly alarmed both the emperor and the pope by his disturbing philo-Turk proclivities. It was owing to Laski's intrigues that the new hospodar of Moldavia, Petrylo, after doing homage to the Porte, intervened in the struggle as the foe of both Ferdinand and Sigismund, and besieged the Grand Hetman of the Crown, Jan Tarnowski, in Obertyn, where, however, the Moldavians (Aug. 22, 1531) sus tained a crushing defeat, and Petrylo was slain. Nevertheless, so anxious was Sigismund to avoid a collision with the Turks, that he forbade Tarnowski to cross the Moldavian frontier, and sent a letter of explanation to Constantinople. On the death of John Zapolya, the Austro-Polish alliance was still further cemented by the marriage of Sigismund's son and heir, Sigismund Augustus, with the archduchess Elizabeth. In the reign of Sigismund was effected the incorporation of the duchy of Masovia with the Polish crown, after an independent existence of 500 years. In 1526 the male line of the ancient dynasty became extinct, and on Aug. 26 Sigismund received the homage of the Masovians at Warsaw, the capital of the duchy and ere long of the whole kingdom.
The Renaissance Era.—The reigns of Sigismund I. and his son Sigismund II. (1548-72) mark the transition from a splendid, but still essentially mediaeval phase of Polish civilization into the heyday of the Renaissance.