Lithuanian-Polish-Russian Commonwealth (Fidem Pacis)

The Lithuanian-Polish-Russian Commonwealth, known as the Republic of Three Crowns or simply Lithuania, was a federal state consisting of Lithuania, Poland and Novgorod, ruled by a common monarch. It was established in 1569 by the Union of Riga, but the personal union between the Kingdom of Lithuania and the Kingdom of Poland actually began in 1386. The Republic of Novgorod joined forty years later in 1420.

At its height the Commonwealth controlled nearly all of eastern Europe. Its three parts were formally equal partners in the union, but over the centuries it was Lithuania which became dominant, both culturally and politically. By the time the union was dissolved in 1921 the vast territory of Western Ruthenia had become mostly Lithuanian-speaking, with the old East Slavic language being made almost extinct.