Lithuanian Civil War ( 1389 – 92 ) 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 the Great . At issue was control of the Grand Duchy of Lithuania , then the largest state in Europe . Jogaila had been crowned King of Poland in 1386 ; he installed his brother Skirgaila as ruler of Lithuania . Skirgaila proved unpopular and Vytautas attempted to depose him . When his first attempt to take the capital city of Vilnius failed , Vytautas forged an alliance with the Teutonic Knights , their common enemy – just as both cousins had done during the Lithuanian Civil War between 1381 and 1384 . Vytautas and the Knights unsuccessfully besieged Vilnius in 1390 . Over the next two years it became clear that neither side could achieve a quick victory , and Jogaila proposed a compromise : Vytautas would become Grand Duke and Jogaila would remain Superior Duke . This proposal was formalized in the Ostrów Agreement of 1392 , and Vytautas turned against the Knights . He went on to reign as Grand Duke of Lithuania for 38 years , and the cousins remained at peace . Background . The family of Gediminas created a state that covered the territories of present - day Lithuania , Belarus , Ukraine , Transnistria , and parts of Poland and Russia . Gediminas died in 1341 ; afterwards his sons Algirdas and Kęstutis , the fathers of Jogaila and Vytautas , co - ruled the Grand Duchy peacefully . However , after Algirdas ' death in 1377 , Kęstutis , Jogaila , and Vytautas began struggling for power . During their first conflict , the Lithuanian Civil War between 1381 and 1384 , Vytautas and Jogaila both struck short - lived alliances with the Teutonic Knights . Vytautas did not manage to seize the throne , and reconciled with Jogaila in 1384 . Jogaila created a significant new alliance with the Polish Kingdom ' s leading noble clans when he secured an agreement to marry the teenage King of Poland Jadwiga of Poland , done in February 1386 and then he was crowned Jure uxoris king of Poland . As a precondition to the marriage , the detailed agreement between the parties known as Union of Krewo was signed in August 1385 ; amongst other conditions agreed to in this document the grand duke was to renounce paganism , become Christian , and Christianize his subjects , and establish a personal union between Poland and Lithuania , the largest state in Christian Europe . The Union was an unwelcome development for the Teutonic Knights , as it united Poland and Lithuania , two states hostile to the Order , and a Christianized Lithuania deprived the Knights of their ideological justification for warring on that state . Thus the Order sought opportunities to undo the Polish – Lithuanian union ; they demanded Samogitia , a section of western Lithuania that bordered the Baltic Sea , and refused to recognize Jogaila ' s baptism in 1386 . Vytautas became duke of Hrodna and Podlaskie ; Jogaila known now by his Christian name Władysław II ( Władysław II Jagiełło ) designated his brother Skirgaila regent in Lithuania . Skirgaila , who also ruled Vytautas ' patrimony in Trakai , was disliked by the Lithuanian nobility . Vytautas , on the other hand , became increasingly popular ; Władysław II began to see him as a rival . Vytautas was supported by Lithuanians who resented the Polish interpretation of the recent Union of Krewo . These Lithuanians wished to maintain distinct legal structures and reserve official posts for Lithuanians . The Lithuanian elites also resented the changes in government that king Władysław II implemented there . Civil war . 1389 – 1390 . Jogaila had sent Klemens Moskarzewski to establish a Polish garrison in Vilnius and stabilize the situation , but this move only angered the opposition . In May 1389 Jogaila tried to mediate the conflict between Skirgaila and Vytautas in Lublin . Vytautas was pressured into signing a formal document declaring that he was loyal to Skirgaila and supported him , but his position as Duke of Lutsk was not formally acknowledged . Vytautas secured his position in Lutsk , and turned his sights on Vilnius . According to Teutonic testimony at the Council of Constance , Vytautas planned to take advantage of his sister ' s wedding by sending wagons filled with meat , hay , and other goods to Vilnius . The wagons would be escorted by armed men , who would capture the castle once inside the city . This plan was uncovered by a German spy and the conspirators were executed . In another setback , two of Vytautas ' strongest allies , his brother Tautvilas and his brother - in - law Ivan Olshanski , lost their territories in Navahrudak and Halshany . Vytautas then sought a military alliance with the Knights , sending captive knight Marquard von Salzbach to negotiate . On January 19 , 1390 in Lyck Vytautas signed the Treaty of Lyck affirming the terms of an earlier agreement , the Treaty of Königsberg , signed in 1384 during his first conflict with Jogaila . Under the terms of this treaty , the Knights were promised Samogitia , up to the Nevėžis River , in exchange for their military assistance . Having been earlier betrayed , the Knights asked for hostages as a guarantee of Vytautas ' loyalty : his brothers Sigismund and Tautvilas , his wife Anna , his daughter Sophia , his sister Rymgajla , his favorite Ivan Olshanski , and a number of other nobles . In May a delegation of 31 Samogitian nobles arrived in Königsberg and promised loyalty to Vytautas by signing the 1390 Treaty of Königsberg . The joint forces of Vytautas and the Teutonic Knights consisted largely of volunteers and mercenaries from western Europe , notably from France , the German states , and England . Henry , Earl of Derby , the future King Henry IV of England and Marshal of France Jean Le Maingre were among the participants . The English crusaders left detailed records of their actions in Prussia and Lithuania , and their exploits were mentioned by Geoffrey Chaucer in the Canterbury Tales , possibly as a compliment to the English knights and the future king . In the meantime , Jogaila achieved some military successes ; his forces captured several castles in Podlaskie , leaving them to be guarded by Polish garrisons , and took Hrodna in April 1390 after a six - week siege . The newly - assembled coalition organized a number of small campaigns in Lithuania ; the largest was undertaken at the end of summer . During this campaign the Knights burned wooden castles at Kernavė , possibly the first capital of Lithuania , which never recovered from the destruction . While the army was laying siege to Georgenburg , Grand Master Conrad Zöllner von Rothenstein died . The coalition decided to abandon this siege and march on Vilnius instead , as such a large army could not easily be re - assembled . On 11 September 1390 the joint forces launched a five - week siege on the city . Vilnius ' castles were held by Skirgaila , commanding combined Polish , Lithuanian , and Ruthenia n troops . The Knights reduced much of the outer city to ruins and managed to destroy the Crooked Castle , which was never rebuilt . Vytautas ' brother Tautvilas Kęstutaitis and Jogaila ' s brother Karigaila died during the siege . The besiegers ran into various difficulties . Their supplies of gunpowder were dwindling , the weather was deteriorating , the terms of service for some volunteers from western Europe ended , and the Knights needed a new Grand Master . They decided to return to Prussia . The siege did not bring an end to the conflict , but it demonstrated an increased dissatisfaction with Jogaila among the regional inhabitants . 1391 – 1392 . On January 21 , 1391 , Vytautas ' only daughter , Sophia of Lithuania , married Vasili I of Russia , Grand Duke of Moscow . This alliance strengthened Vytautas ' influence in Slavic lands and represented a potential new ally against Poland . At the same time , Jogaila ' s brother Lengvenis was losing his power in Veliky Novgorod to Moscow . The Teutonic Knights were idled during the protracted selection of their new Grand Master , Konrad von Wallenrode ; their general chapter delayed his election . In May 1391 the new master mortgaged Złotoria ( Slatoria ) , a castle near Thorn , from Władysław Opolczyk , count palatine of Sigismund of Hungary , for 6 , 632 guldens . This angered Jogaila and he invaded Dobrzyń Land , but was driven away . Von Wallenrode called for new volunteers from France , England , and Scotland . Among those who responded was William Douglas of Nithsdale . During the autumn of 1391 the Teutonic Knights organized another campaign against Vilnius . In Kaunas they organized a lavish feast , which was prominently featured in " Konrad Wallenrod " , an 1828 poem by Adam Mickiewicz . They devastated the nearby towns of Ukmergė and Maišiagala , but lacked the resources for a second siege on Vilnius . In November 1391 Vytautas attacked the areas near Merkinė and Hrodna , cutting off the easiest communication route between Jogaila and Skirgaila . In the meantime the Knights were buying lands in Prussia . In May 1392 von Wallenrode began negotiations with Sigismund of Hungary to buy Neumark for 500 , 000 guldens . Negotiations fell apart as the title to the land was contested by several dukes . The Neumark purchase was closed with Jobst of Moravia only in 1402 . During July 1392 the Knights agreed to pay Władysław Opolczyk 50 , 000 guldens for the Dobrzyń Land , which had been contested among Piast dukes since 1377 . Opolczyk , the ruler of Opole in Silesia , had little interest in the volatile regions to his north . In 1392 he circulated a proposal to partition Poland among the Teutonic Knights , the Holy Roman Empire , Silesia , and Hungary , but it was rejected . These purchases by the Knights threatened Poland ' s northern borders . Neither Jogaila nor Vytautas had gained a clear advantage and the territories of the Grand Duchy affected by the civil war were being devastated . Polish nobles were dissatisfied with the war ; Jogaila was spending a great deal of time on Lithuanian matters and the expected benefits of the Union of Krewo had not materialized . The Union was meant to strengthen Polish control over Galicia , Moldavia , and Wallachia rather than to create fresh troubles in the north . Jogaila was preoccupied with the management of his court , battles in the southeast , and his sickly wife . He attempted to replace Skirgaila with his younger brother Vygantas , but this brother died under unclear circumstances – according to rumor he was poisoned by either Vytautas or Skirgaila . Klemens Moskarzewski was replaced with Jan Oleśnicki from Kraków as governor of Vilnius . Jogaila decided to seek a compromise with Vytautas . Peace treaty . In spring 1392 Jogaila proposed a compromise through his envoy , Henry of Masovia , Bishop of Płock : Vytautas would become the Grand Duke of Lithuania if he would recognize Jogaila as supreme duke . By summer Vytautas had secured the release of many of the hostages he had given to the Knights , and accepted the offer . Since this agreement with Jogaila was reached in secret , the Knights suspected nothing when Vytautas invited them to the festivities at his headquarters , the Ritterswerder Castle on an island in the Neman River . Most of the prominent guests were taken prisoner and Vytautas ' army proceeded to attack and destroy the undermanned wooden castles of Ritterswerder , Metenburg , and Neugarten ( New Hrodna ) near Hrodna . The Ostrów Agreement , formalizing the arrangement and ending the civil war , was signed on August 4 , 1392 . Vytautas became Grand Duke and reclaimed his patrimony in Trakai while Skirgaila was compensated with the Principality of Kiev , where he died in 1397 . While Vytautas was technically a vassal of Jogaila , he exercised considerable power in the Grand Duchy . His independence was legalized in the 1401 Union of Vilnius and Radom . Vytautas ruled Lithuania until his death in 1430 ; his relationship with Jogaila during these years is sometimes likened to the peaceful power - sharing demonstrated by their fathers Algirdas and Kęstutis . The Knights , betrayed for the second time , resumed their wars against Lithuania . They sought to take Samogitia , which Vytautas had twice promised them . The Treaty of Salynas was signed in 1398 , leaving Samogitia to the Knights , to quiet the Duchy ' s western front while Vytautas was organizing a major campaign against the Golden Horde . Vytautas suffered a major defeat at the Battle of the Vorskla River in 1399 . The cousins joined their forces at the Battle of Grunwald in 1410 , which ended the threat from the Teutonic Orders .