Editing Władysław III of Poland (section)

===Civil war in Lithuania, 1434–1438===
{{further|Polish–Teutonic Wars}}
[[File:Wladyslaw III, King of Poland.jpg|thumb|right|Władysław portrayed in a prayerbook held at the [[Bodleian Library]] in [[University of Oxford|Oxford]], 15th century.]]

Władysław faced certain challenges early in his reign, in particular the inherited situation in the Grand Duchy of Lithuania was precarious and the ensuing [[Lithuanian Civil War (1432–1438)]] threatened Polish interests there. The conflict began when Władysław's paternal uncle, [[Švitrigaila]], refused to acknowledge [[fealty]] to his brother Jogaila and proclaimed political independence, jeopardising the [[Polish–Lithuanian union]].{{sfn|Kiaupienė|2008|pages=205–211}} He subsequently battled against Polish–Lithuanian forces in [[Volhynia]] and established an anti-Polish coalition.{{sfn|Sužiedėlis|1970–1978|pages=348–350}} In June 1431, he reached an agreement with the [[Teutonic State]], which declared a surprise war and marched its army into Polish territory.{{sfn|Gieysztor|1998|pages=734–735}} Following a [[truce]] with the [[Teutonic Knights]], the war resumed when Władysław became king. The situation swiftly transformed into a diplomatic struggle for Władysław and the Poles, who sought to turn Lithuanian nobles against Švitrigaila and have him ousted.{{sfn|Kiaupienė|2008|pages=205–211}}

A Polish retinue of approximately 4,000 men under [[Jakub Kobylański]] assisted the Lithuanians headed by Sigismund Kęstutaitis and [[Michael Žygimantaitis]]; their joint army defeated Švitrigaila and his allies, [[Sigismund Korybut]] and the [[Livonian Order]], on 1 September 1435 at the [[Battle of Wiłkomierz]].{{sfn|Mačiukas|2015}} Švitrigaila fled eastward, but eventually lost the support of the [[Ruthenians]] residing in the Grand Duchy and went into exile to [[Moldavia]] in 1438, thus ending civil war.{{sfn|Sužiedėlis|1970–1978|pages=348–350}} However, unrest re-emerged when Sigismund Kęstutaitis was assassinated on 20 March 1440 and Władysław's younger brother, [[Casimir IV Jagiellon|Casimir]], was proclaimed Grand Duke by [[Jonas Goštautas]] and the [[Lithuanian Council of Lords]] on 29 June 1440.{{sfn|Sužiedėlis|2011|page=71}}{{sfn|Scott|2015|page=393}} This was met with hostility at the Polish court, especially that Casimir was underage and that the Poles hoped for a [[vicegerent]] that would submit to Poland.{{sfn|Scott|2015|page=393}} Regardless of the outcome, Władysław continued to use the title of Supreme Duke of Lithuania until death under the conditions of the 1413 [[Union of Horodło]].{{sfn|Mikulec|Polívka|2007|page=248}}{{sfn|Kiaupa|2000|pages=154–155}}

The battle also proved momentous in combating the Livonian Order as its [[Livonian Order#Masters of the Livonian Order|Grand Master, Franco Kerskorff]], and [[Commander (order)|''komtur'' commanders]] were killed or taken prisoner.{{sfn|Kiaupienė|2008|pages=205–211}}{{sfn|Urban|2003|pages=311–313}} The [[Livonian Confederation]] agreement from 4 December 1435 officially terminated its crusading character, and a [[Peace of Brześć Kujawski|formal peace treaty was signed on 31 December 1435]] in [[Brześć Kujawski]] whereby the Teutonic and Livonian Orders pledged not to intrude or disturb the internal affairs of both Poland and Lithuania.{{sfn|Spórna|Wierzbicki|Wygonik|2004|page=468}}{{sfn|Błachowska|2009|page=325}} That act concluded the [[Polish–Teutonic War (1431–1435)]].{{sfn|Błachowska|2009|page=325}} Moreover, any association between the knights and the [[Pope]] or the [[Holy Roman Emperor]] would violate the treaty.{{sfn|Jasienica|1978|page=142}} His youth prvented Władysław from engaging directly in the peace talks, and the negotiations were predominantly undertaken by diplomats or the [[clergy]].{{sfn|Reddaway|Penson|Halecki|Dyboski|1950|page=235}}