At the beginning of the 13th century, the Polotsk Principality encountered the aggression of the Crusaders. Polotsk Prince Vladimir devoted almost half of his reign to the struggle against the German knights. The allies of Polotsk in that struggle at various times were Livs, Latgalians, Estes and Lithuanians. In 1239 the military-political union of Polotsk with Novgorod was concluded through a dynastic marriage between Alexander Yaroslavich and the daughter of the Polotsk prince Bryachislav.
In the middle of the 13th century the first Lithuanian princes appeared in Polotsk, but the Polotsk land finally entered the Grand Duchy of Lithuania only in 1307.For a whole century, Polotsk remained the center of a large Principality. The entry of Polotsk into the Grand Duchy of Lithuania coincided with the period of its most active confrontationto the aggression of the Teutonic Order. During the reign of the last Polotsk prince Andrey Olgerdovich (the second half of the 14th century) the city withstood five large sieges of the Crusaders. On 15 of June, 1410 about 1500 warriors took part in the Battle of Grunwald under the command of Ivan Nemira. The victory gained in that battle by the combined forces of the Grand Duchy of Lithuania and Poland was the end of almost two centuries of fighting