Lithuanian Civil War
The Lithuanian Civil War of 1389–1392 was the second civil conflict between Jogaila, King of Poland and Grand Duke of Lithuania, and his cousin Vytautas. At issue was control of the Grand Duchy of Lithuania, then the largest state in Europe. Wikipedia
End date: 1392
Result: Ostrów Agreement; Jogaila was designated Supreme Duke and Vytautas Grand Duke
Start date: 1389
Location: Lithuania, Grand Duchy of Lithuania, and Prussia