Teutonic Knight - Tannenberg 1410

Formed at the end of the 12th century in Acre, in the Levant, the medieval Order played an important role in Outremer, controlling the port tolls of Acre. After Christian forces were defeated in the Middle East, the Order moved to Transylvania in 1211 to help defend the South-Eastern borders of the Kingdom of Hungary against the Kipchaks. The Knights were expelled by force of arms by King Andrew II of Hungary in 1225, after attempting to place themselves under papal instead of the original Hungarian sovereignty and thus to become independent.
In 1230, following the Golden Bull of Rimini, Grand Master Hermann von Salza and Duke Konrad I of Masovia launched the Prussian Crusade, a joint invasion of Prussia intended to Christianize the Baltic Old Prussians. The Knights had quickly taken steps against their Polish hosts and with the Holy Roman Emperor's support, had changed the status of Chelmno Land (also Ziemia Chelminska or Kulmerland), where they were invited by the Polish prince, into their own property. Starting from there, the Order created the independent Monastic State of the Teutonic Knights, adding continuously the conquered Prussians' territory, and subsequently conquered Livonia. Over time, the kings of Poland denounced the Order of holding lands rightfully theirs, specifically Chelmno Land and Polish lands that would be conquered later, such as Pomerelia (also Pomorze Gdanskie or Pomerania), Kujawy, and Dobrzyn Land.
The Order theoretically lost its main purpose in Europe with the Christianization of Lithuania. However, it initiated numerous campaigns against its Christian neighbours, the Kingdom of Poland, the Grand Duchy of Lithuania, and the Novgorod Republic (after assimilating the Livonian Order). The Teutonic Knights had a strong economic base, and so hired mercenaries from throughout Europe to augment their feudal levies, and became a naval power in the Baltic Sea. In 1410, a Polish-Lithuanian army decisively defeated the Order and broke its military power at the Battle of Grunwald (Tannenberg). However, the capital of the Teutonic Knights was successfully defended in the following Siege of Marienburg and the Order was saved from collapse. -Wikipedia-