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Background
The Teutonic order played an exceptionally important role in the history of the crusading movement and in the political, economic, and cultural development of northeastern Europe. It was an important part of the military orders in Medieval history. However, this German order didn’t have such a big impact when compared with the Templars and Hospitallers.
History
The start
In 1190, the merchant of Lübeck and Bremen established a hospital at Acre, the predecessor of the Teutonic order was born. Just like other hospitals, it provided medical care for German Christian pilgrims.
Because the military power developed very fast in the next several years, the pope Innocent III allowed it became a military order ——the Teutonic order in 1199 and followed the rule of the Knights Templar.
The development
In 1211, the King of Hungary Andras II asked them to against Comans.
The Teutonic knights wanted to build their country in Hungary, but they were expulsed by Andras II in 1225.
In 1229, the Teutonic knights accepted the request from Conrad and joined the war to the Prussians, and Conrad gave them Kulmerland as the reward.
In the same year, the German King Frederick II led his crusades to Egypt. The result is that hey got a ten-year truce agreement with Sudan and Christians could go to Jerusalem.
In 1237, it had a great era of town foundations.
In the same year, they wanted Russians to change their Church but failed.
In 1260, the Battle of Durben. This German order lost the war to Lithuanians.
Unfortunately, in 1291, their headquarters in Acre fell. Then, they moved to Venice.
The 14th century was the most powerful period of the Teutonic Order.
From 1326 to 1333, the Teutonic Order invaded Poland, and Poles had to surrender.
The decline
In 1386, Poland and Lithuania became a barrier to the Teutonic Order.
On 15 July 1410, the leader of the Teutonic order Jungingen was defeated by the Polish-Lithuanian army at Tannenberg.
In 1451, the Teutonic order only had two hundred twenty-six Knights, four hundred two priests, and thirty-two Sariant Brothers.
In 1466, the Teutonic state was ruled by the King of Poland.
In 1525, they lost their most valuable thing and never made a comeback. The Teutonic states had lands from the Baltic to the Black sea.

https://www.researchgate.net/publication/242115647_PRUSSIAN_LANDS_THROUGHOUT_THE_AGES_-_TERRITORIAL_AND_POLITICAL_CHANGES

https://library.artstor.org/#/asset/BARTSCH_2770019
Successive leaders
1.Heinrich Walpot von Bassenheim(1198-1200): He was the first Grand Master of the Teutonic Order. He turned the Teutonic organization to a military order and got the privilege from the pope Innocent III.
2. Hermann von Salza (1209-1239): He led the Prussian Crusade in 1230, and started the annual military invasion to Prussians.
3.Heinrich von Plauen: He held the Marienburg from the Polish-Lithuanian army’s attack after the Teutonic Order was defeated at Tannenberg.
Resource
Robert A, Selig. “THE BATTLE OF TANNENBERG-Teutonic Knights and Six Hundred Years of German-Polish History.” German Life, 2010. July 22. https://search.proquest.com/docview/312272396/C51298BF7E1F4730PQ/8?accountid=11235#center
https://search.proquest.com/docview/1974775442?accountid=11235&pd=1974847868
Thomas F. Madden. “The concise history of the Crusades” Chapter 7
https://search.proquest.com/docview/1974775431?accountid=11235&pd=1974775442