Few battles are as important to German history as the battle of Tannenberg, or Grunwald. Fought on July 15th, 1410, the Battle of Tannenberg saw the forces of Poland and Lithuania crush the army of the Teutonic Order, and so permanently break their power in the region.
In 1409, the territory of Samogita revolted against its Teutonic occupiers. Samogita had been part of the grand Duchy of Lithuania, and The Kingdom of Poland declared that it would support Lithuania in retaking the territory. The Grand Master of the Teutonic Order, Ulrich von Jungingen, declared war on Poland and Lithuania. He then invaded Poland, and following some small-scale fighting, signed a truce which would expire on the 24th of June, 1410. Both sides spent the length of the truce mustering their armies and securing allies. The King of Poland and the Duke of Lithuania, Władysław II Jagiełło and Vytautas, agreed to combine their armies and march in force on the Order’s capitol, Marienburg. The Teutonic Order were informed of this plan when Hungarian envoys informed Ulrich. On July 11th, two days after the Polish-Lithuanian army crossed the border into Teutonic territory, the grand Master decided with his council of war to meet the enemy in battle. On July 15th, the two armies met. The Polish placed their heavy cavalry on their left flank and the Lithuanian their light cavalry on the right. Mercenary infantry made up the center. The Teutonic Order massed its heavy cavalry against the Lithuanians, hoping to drive them from the field and then flank the infantry. The battle began with a Lithuanian attack on the Teutonic left flank. This attack failed, and the Lithuanians retreated. Some consider this retreat to be a planned feigned retreat, while others think it was a rout of the Lithuanian army. In any case, during the retreat the Polish and Teutonic armies clashed. The two armies fought inconclusively for several hours until the Lithuanian cavalry returned and attacked the Teutons from the rear. Jungingen was killed and the Order’s forces began to retreat. However, their camp followers turned on them and their attempt to construct a wagon fort failed, ending in the slaughter of most of their army.
The Teutonic Order would never again be the dominant power in North-Eastern Europe. Most of its army was destroyed and, although it was not made to give up much territory, a massive war indemnity was imposed upon it. This indemnity weakened the Teutonic economy. Further, after Poland and Lithuania became more fully Christianized, it became far harder to recruit crusaders, forcing the Order to rely on mercenaries, which further strained its finances. The Teutonic Order would survive until the next century, but the Battle of Tannenberg was the cause of its decline and, eventually, its end as a state.