War of the Flemish Succession The War of the Flemish Succession was a series of feudal conflicts in the mid - thirteenth century between the children of Margaret II , Countess of Flanders . They concerned the succession to the two counties , the first a fief of the King of France and the latter of the King of Germany . Origins . When Baldwin IX , Count of Flanders and Hainault , left on the Fourth Crusade in 1202 , he left his western domains under his eldest daughter Joanna . Joanna inherited the counties on Baldwin ' s death and , despite two marriages , died without heirs in 1244 . She was succeeded by her younger sister , the aforementioned Margaret . Margaret ' s first marriage , to Bouchard of Avesnes , was broken in 1221 per orders from Joanna and the excommunication of Bouchard . By Bouchard , however , she had already had three children , including John I of Avesnes . Nevertheless in 1223 , Margaret remarried with William II of Dampierre ( d . 1231 ) , who likewise gave three offspring , including William III and Guy of Dampierre . The rights to Margaret ' s inheritance between the sons of Avesnes and those of Dampierre were the cause of the conflicts known as the " war of the succession of Flanders and Hainault . " First conflict . The first conflict opened with Margaret ' s succession in 1244 . John I of Avesnes and William of Dampierre , half brothers , fought between themselves until King Louis IX intervened in 1246 . Louis gave Hainault ( technically not his to give ) to John I of Avesnes and Flanders ( indeed his vassal ) to William of Dampierre . Margaret , in light of this judgement , gave the government of Flanders over to William of Dampierre in 1247 . She did not however relinquish her governance of Hainault to John I of Avesnes . In 1251 , William III of Dampierre died and Flanders passed to his brother Guy of Dampierre . Second conflict . In 1248 , Louis had left on the Seventh Crusade and remained abroad for six years . John I of Avesnes quickly apprehended that his mother did not intend to give him the government of Hainault as she had that of Flanders to her other sons . John I of Avesnes revolted against his mother and attacked his half - brother Guy of Dampierre , recently become count of Flanders . The war continued with John I of Avesnes convincing the German anti - king William of Holland , to seize Hainault and Flemish territory within the empire . The fighting continued until the Battle of West - Capelle of 4 July 1253 , where John I of Avesnes gained a brilliant victory over Guy of Dampierre and forced him and his mother to respect the division of Louis and grant him Hainault . Third conflict . Margaret did not rest in her defeat and did not recognise herself as overcome . She instead granted Hainault to Charles of Anjou , the brother of King Louis , who had recently returned from the crusade . Charles took up her cause and warred with John I of Avesnes , but failed to take Valenciennes and just missed being killed in a skirmish . When Louis returned in 1254 , he reaffirmed his earlier arbitration and ordered his brother to get out of the conflict . Charles returned to Provence . With this second arbitration of the holy king , the conflict closed and John I of Avesnes was secure in Hainault .