Mazovia

The Duchy of Mazovia arose from the partition of Poland in 1138 and was ruled by a branch of the Piast dynasty. After another division in 1313, Siemowit III reunited most of its lands and became a Polish vassal in 1351.

The duchy was divided again in 1381; Janusz I moved his residence from Czersk to Warsaw in 1413. In 1526 the death of Janusz III ended the male Masovian Piast line, and Poland incorporated the duchy despite resistance from some local nobles.