Poland ceased to be a haven for the sons of Judah, when its short-sighted kings summoned the Jesuits to supervise the training of the young nobles and the clergy and crush the spirit of the Polish dissidents. These originators of disunion, to whom the frequent partition of Poland must be attributed, sought to undermine the unobtrusive power which the Jews, through their money and prudence, exercised over the nobles, and they combined with their other foes, German workmen and trades-people, members of the guilds, to restrict and oppress them. After that time there were repeated persecutions of Jews in Poland; sometimes the German guild members, sometimes the disciples of2 the Jesuits, raised a hue and cry against them. Still, in the calamities of the Thirty Years' War, fugitive Jews sought Poland, because the canonical laws against Jews were not applied there with strictness. The high nobility continued to be dependent on Jews, who in a measure counterbalanced the national defects. Polish flightiness, levity, unsteadiness, extravagance, and recklessness were compensated for by Jewish prudence, sagacity, economy, and cautiousness. The Jew was more than a financier to the Polish nobleman; he was his help in embarrassment, his prudent adviser, his all-in-all. Especially did the nobility make use of Jews in developing recently established colonies, for which they had neither the necessary perseverance nor the ability. Colonies had gradually been formed on the lower Dnieper and the northern shore of the Black Sea, by runaway Polish serfs, criminals, adventurers from every province, peasants, and nobles, who felt themselves cramped and endangered in their homes. These outcasts formed the root of the Cossack race at the waterfalls of the Dnieper (Za-Porogi), whence the Cossacks obtained the name of Zaporogians. To maintain themselves, they took to plundering the neighboring Tartars. They became inured to war, and with every success their courage and independent spirit increased.