[1] After the demise of Gediminas in December 1337, the Duchy of Lithuania was divided into two parts: Grand Duke Algirdas ruled Vilnius and the Eastern Aukštaitija while his brother Kęstutis received the Duchy of Trakai.

[1][2] The ruler of the Duchy of Vilnius also was the Grand Duke of Lithuania.

[2][3] In 1382, during the Lithuanian Civil War, Kęstutis was imprisoned at the Kreva Castle and died.

Vytautas, son of Kęstutis, then waged a new Lithuanian Civil War to regain his patrimony in Trakai and seize power in Lithuania.

One could delineate the boundaries of the Duchy of Trakai by referring to the donative writ of Grand Duke Jogaila: from the Livonian border (Upytė) to Kobrynin (Masuria), and eastward from Podlesie to Pinsk.