began his preparation in October and November 1625 by settling in the Halberstadt-Aschersleben area and extending its borders. Wallenstein and the growing Imperial Army were informed of the approach of Mansfeld and his Danish army. King Christian IV of Denmark had formally entered Denmark into the Thirty Years War. As Mansfeld and his army was commanded to approach Albrecht von Wallenstein at the Dessau Bridge, King Christian IV of Denmark and ally Christian of Brunswick were commanded to fight the Catholic army of the Count of Tilly in Upper Austria. Christian of Brunswick's engagements at Fleurus, Höchst in 1622, and the Battle of Stadtlohn in 1623 were not victorious, and the battles diminished his force. Christian of Brunswick and his peasant Protestant army, backing the army of King Christian of Denmark, was soon eliminated by the Catholics due to the weakness of his army and lack of a supporting army from Landgrave when moving into Hesse. Part of the Imperial Army, under the command of Johann von Aldringen, had time to prepare heavy artillery and troops for any Protestant threat advancing down the Elbe. Wallenstein and the Imperial Catholic league marched to Dessau, where Mansfeld and the Protestant army would inevitably try to cross in order to reach Magdeburg and the German Catholic League headquarters in Aschersleben. In Vienna, there was talk of Wallenstein's deposition from his army and replacement by the Italian, Count Collalto, an expert in the art of mercenary leadership.
Battle and Outcome
In April 1625, Mansfeld and his army moved as quickly as possible to Dessau, as did Wallenstein and the Imperial Army. Aldringen and his men arrived first, thus allowing them to form their "death trap" at the Dessau Bridge, deploying the heavy artillery which they possessed. Due to Wallenstein's inexperience, Mansfeld was overly confident and underestimated his enemy as his army approached. Mansfeld was not aware that they were soon to face the most powerful and deceivingly large army along the river bank of the Elbe. On 25 April, the battle began and the troops of Aldringen held off Mansfeld and his troops as they attempted to push across the bridge and river. The Imperial army was in soon in heavy force by the arrival of Wallenstein and troops. Mansfeld and his troops were completely overpowered. As soon as nearly half of Mansfeld's army was destroyed, the Danes retreated to Silesia. Mansfeld was able to rebuild his army with the help from John Ernest I, Duke of Saxe-Weimar and an army of 7,000, which gave him a similar sized army which he had lost half of at Dessau. His rally did not last long as he died outside a village in Sarajevo soon before his ally, Johann Ernst. The Danish Protestant army fell apart and retreated into Upper Silesia. Christian IV's army was defeated by the Count of Tilly in the Battle of Lutter, which left Tilly with the lands of Holstein, Jutland, and Schleswig.
