The battle of Barenberg (near Lutter, August 1626) gave the Imperialists the upper hand in North Germany. This ascendancy was taken away from them, however, with the appearance of Gustavus Adolphus of Sweden, who won a complete victory over Tilly in the battle of Breitenfeld (September 17, 1631). After that, Gustavus Adolphus advanced to the Lower Main (Frankfurt and Mayence), and the following year carried the war into Bavaria, which now became the principal scene of the fighting. After the battle of Nördlingen (September 7, 1634), the fugitive Swedish Protestant army, pursued by the Imperialists, retreated through Württemberg, Baden, and Hesse to the Rhine, where the war was now carried on for several years. Both armies were badly infected with disease, and spread pestilence wherever they went. After the battle of Nördlingen the war became decentralized, splitting up into a number of warlike movements throughout all Germany; and everywhere these movements occurred they added, if possible, to the misery of the people. In the year 1631 that terrible epoch of plague began which reached its climax in the years 1634–5 and lasted well into the following year. Its widespread character was due to the innumerable plundering and devastating marches of the Protestant-Swedish and Imperialist-Catholic armies back and forth across the country, and also to the consequent famine. Everything the brutalized soldiers could not consume themselves or take with them, they destroyed or burned. There was an absolute dearth of farm-workers, and in addition to that, the year 1635 was dry and unproductive. Horrible are the descriptions of the hunger and misery which the people in all parts of Germany experienced at that time. Under such conditions pestilences could spread unhindered; to be sure, they relaxed a little after the year 1638, but by no means ceased entirely. Whenever real plague disappeared, typhus fever, which was prevalent in all parts of the army took its place; and thus diseases were borne from place to place until the very end of that disastrous war. I. THE WAR IN BOHEMIA AND THE PALATINATE (1618–24)