From 1620 to 1631, he won an unmatched and demoralizing string of important victories against the Protestants, including White Mountain, Wimpfen, Höchst, Stadtlohn and the Conquest of the Palatinate.

Along with Duke Albrecht von Wallenstein of Friedland and Mecklenburg, he was one of two chief commanders of the Holy Roman Empire’s forces during the first half of the Thirty Years' War.

Johann Tserclaes was born on February 1559 in Castle Tilly, Walloon Brabant, in the Spanish Netherlands, in what is now Belgium, to a devoutly Catholic Brabantine family.

After receiving a Jesuit education in Cologne, he joined the Spanish Army at the age of fifteen and fought under Alexander Farnese, Duke of Parma in his campaign against the rebellious Dutch forces during the Eighty Years' War, participating in the successful Siege of Antwerp in 1585.

After this he joined the Holy Roman Empire's campaign against the Ottoman Turks in Hungary and the Transylvania as a mercenary during the Long Turkish War in 1600, and through rapid promotion became a field marshal in only five years.

[1] As commander of the forces of the Catholic League, Tilly fought against the Bohemian rebels following the Defenestration of Prague, by which time he had trained his soldiers in the Spanish Tercio system, which featured musketeers supported by deep ranks of pikemen.

A force of 25,000 soldiers, including troops of both the Catholic League and the Emperor scored an important victory against Christian of Anhalt and Count Thurn at the decisive Battle of White Mountain west of Prague on 8 November 1620.

This caused King Christian IV of Denmark to enter the Thirty Years' War in 1625 to protect Protestantism, and also in a bid to make himself the primary leader of Northern Europe.

Count Tilly besieged and captured Münden on 30 May 1626, whereupon local and refugee Protestant ministers were thrown into the river Werra, but could not lay a siege to Kassel.

[2] While Gustavus Adolphus landed his army in Mecklenburg and was in Berlin, trying to make alliances with the leaders of Northern Germany, Tilly laid siege to the city of Magdeburg on the Elbe, which promised to support Sweden.