Pressured by the crusading Teutonic Knights and Livonian Knights, the Lithuanian tribes united around 1250. Under the rule of Gediminas (ruled 1316-41) a strong, cohesive Grand Duchy emerged. One of his sons, Algirdas, conquered vast Russian and Tartar territories. His domain stretched all the way from the Baltic to the Black Sea.

The grand duke Jagiello (or Jogaila) conducted a pact with Poland (1386) in which he agreed to accept the Roman Catholic faith, marry the Polish queen, become king of Poland, and unite Poland and Lithuania under a single ruler.

Lithuania continued to have its own rulers, but in 1569 they were compelled to accept the Union of Lublin, which established a Polish-Lithuanian confederation. Eventually Lithuania became an integral part of Poland until the 18th century, when the partitions of Poland placed it in the Russian Empire.