The Teutonic Order is an order of knights that, while founded in Jerusalem, is most famous for its efforts to Christianize Eastern Europe and for later wars with the Kingdom of Poland. The Teutonic Order controlled much of modern day Prussia and Pomerania for hundreds of years, but by the 15th century had come under the suzerainty of the Kingdom of Poland. The members of the Order resented this and also the Polish occupation of “Royal Prussia ”, the Eastern half of Prussia, and so refused to help the Poles in their war with Russia and further demanded the return of territories and an indemnity for their occupation. The Polish Parliament, or Sejm, flatly refused this demand and declared war on the Teutonic Order in 1519. The war was rather inconclusive, with several cities changing hands and both sides launching offensives which were unable to decisively defeat the enemy. It only ended in 1521 when the Holy Roman Emperor Charles V forced an end to hostilities so as to unite Europe against the Ottomans, who had just invaded Hungary. The Teutonic Order and Poland agreed to the Compromise of Tolun, which established a four year truce in which to decide whether the Grand Master of the Teutonic Order, Albert of Hohenzollern, would have to reaffirm his fealty to Sigismund I of Poland. The two states were unable to reach an agreement during the truce, however, and Albert attempted to find allies to aid him when the war resumed. One of the people he met was Martin Luther, who convinced Albert to convert to Protestantism and made Teutonic controlled Prussia into his own personal Duchy of Prussia, which would be the first Protestant state. Albert resigned as Master of the Teutonic Order on April 10th and made himself Duke of Prussia. The Prussian Landtag, an assembly of nobles and property owners which had always opposed Teutonic rule, agreed with this action and accepted the Protestant Reformation. In 1525 the Duchy of Prussia was created. The Teutonic Order selected a new Grand Master and attempted to regain Prussia by political means, but were unsuccessful and would gradually decline until ceasing to be a political entity.
The Duchy of Prussia would grow in power over the next two centuries, taking control of all of Prussia and later most of East Germany and sections of Poland. It was elevated to a Kingdom in 1701 after the War of the Spanish Succession. The Kingdom of Prussia would, along with Austria and Russia, destroy Poland and partition its territory. In 1871 the Kingdom of Prussia would, along with the other remaining German States, form the German Empire. The course of Prussian history is quite remarkable. Prussia went from a breakaway Duchy of a fading order to the most powerful state in Germany to the most powerful nation on the European continent. This improbable course of history all started on April 10th, 1525, when the Grand Master of the Teutonic Order declared himself Duke of Prussia.