The Battle of Grunwald, Battle of Žalgiris, or First Battle of Tannenberg, was fought on 15 July 1410 during the Polish–Lithuanian–Teutonic War. The alliance of the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania, led respectively by King Władysław II Jagiełło (Jogaila), and Grand Duke Vytautas, decisively defeated the German Teutonic Order, led by Grand Master Ulrich von Jungingen. Most of the Teutonic Order's leadership were killed or taken prisoner.

Although defeated, the Teutonic Order withstood the subsequent siege of the Malbork Castle and suffered minimal territorial losses at the Peace of Thorn (1411), with other territorial disputes continuing until the Treaty of Melno in 1422. The order, however, never recovered their former power, and the financial burden of war reparations caused internal conflicts and an economic downturn in the lands controlled by them. The battle shifted the balance of power in Central and Eastern Europe and marked the rise of the Polish–Lithuanian union as the dominant regional political and military force.

The battle was one of the largest in medieval Europe. The battle is viewed as one of the most important victories in the histories of Poland and Lithuania. It is also commemorated in Ukraine and Belarus. It has been used as a source of romantic legends and national pride, becoming a larger symbol of struggle against foreign invaders. During the 20th century, the battle was used in Nazi German and Soviet propaganda campaigns. Only in recent decades have historians moved towards a dispassionate, scholarly assessment of the battle, reconciling the previous narratives, which differed widely by nation.
What was the result and impact of the First Battle of Tannenberg?
The Teutonic Order was defeated in the First Battle of Tannenberg and the subsequent decline of the Teutonic Order led to Polish–Lithuanian union becoming the dominant regional force.