 In 1430, after the death of Vytautas, Mykolas Kęsgaila and his brothers Rumbaudas and Jaunius Valimantaitis supported the accession of Švitrigaila to the Lithuanian throne.He signed the Treaty of Skirsnemunė of 1431 – alliance of Švitrigaila with the Teutonic Knights during the Lithuanian Civil War (1432–38).After Sigismund Kęstutaitis seized power, Mykolas and his brothers were imprisoned.