When Joachim undertook the government of Brandenburg he had to deal with an amount of disorder almost as great as that which had taxed the energies of Frederick I. a century before. Highway robbery was general, the lives and property of traders were in continual jeopardy, and the machinery for the enforcement of the laws was almost at a standstill. About 1504 an attack of unusual ferocity on some Frankfort traders aroused the elector's wrath, and during the next few years the execution of many lawbreakers and other stern measures restored some degree of order. In this and in other ways Joachim proved himself a sincere friend to the towns and a protector of industry. Following the economic tendencies of the time he issued sumptuary laws and encouraged manufactures; while to suppress the rivalry among the towns he established an order of precedence for them. Equally important was his work in improving the administration of justice, and in this direction he was aided by scholars from the university which he had founded at Frankfort-on-Oder in 1506. He gave a new organization to the highest court of justice, the _Kammergericht_, secured for himself an important voice in the choice of its members, and ordered that the local law should be supplemented by the law of Rome. He did not largely increase the area of Brandenburg, but in 1524 he acquired the county of Ruppin, and in 1529 he made a treaty at Grimnitz with George and Barnim XI., dukes of Pomerania, by which he surrendered the vexatious claim to suzerainty in return for a fresh promise of the succession in case the ducal family should become extinct. Joachim's attitude towards the teaching of Martin Luther which had already won many adherents in the electorate, was one of unrelenting hostility. The Jews also felt the weight of his displeasure, and were banished in 1510.
Ignoring the _Dispositio Achillea_, the elector bequeathed Brandenburg to his two sons. When he died in July 1535 the elder, Joachim II., became elector, and obtained the old and middle marks, while the younger, John, received the new mark. John went definitely over to the side of the Lutherans in 1538, while Joachim allowed the reformed doctrines free entrance into his dominions in 1539. The elector, however, unlike his brother, did not break with the forms of the Church of Rome, but established an ecclesiastical organization independent of the pope, and took up a position similar to that of King Henry VIII. in England. Many of the monasteries were suppressed, a consistory was set up to take over the functions of the bishops and to act as the highest ecclesiastical court of the country. In 1541 the new ecclesiastical system was confirmed by the emperor Charles V. With regard to this policy the elector was probably influenced by considerations of greed. The bishoprics of Brandenburg, Havelberg and Lebus were secularized; their administration was entrusted to members of the elector's family; and their revenues formed a welcome addition to his impoverished exchequer. Nor did Joachim neglect other opportunities for adding to his wealth and possessions. In 1537 he had concluded a treaty with Frederick III., duke of Liegnitz, which guaranteed to the Hohenzollerns the succession to the Silesian duchies of Liegnitz, Brieg and Wohlau in the event of the ducal family becoming extinct; this arrangement is important as the basis of the claim made by Frederick the Great on Silesia in 1740. The treaty was declared invalid by the German king, Ferdinand I.; but the elector insisted on its legality, and in 1545 strengthened his position by arranging a double marriage between members of his own family and that of Duke Frederick. Of more immediate consequence was an arrangement made in 1569 with the representatives of Joachim's kinsman, Albert Frederick, duke of Prussia, after which the elector obtained the joint investiture of the duchy of Prussia from Sigismund II., king of Poland, and was assured of the succession if the duke's family became extinct. Joachim's luxurious habits, his partiality for adventurers, and his delight in building, led him to incur such a heavy expenditure that after pledging many of his lands and rights he was compelled in 1540 to appeal for help to the estates. Taking advantage of his difficulties, the estates voted him a sum of money as the price of valuable concessions, the most important of which was that the elector should make no alliance without their consent. Fresh liabilities were soon incurred, and in spite of frequent contributions from the estates Joachim left at his death in January 1571 a heavy burden of debt to his son and successor, John George.