Excerpts from Books and Wikipedia
"He was strongly influenced by the writings of the English reformer John Wycliffe (c.1329-1384), and he criticized the wealth of the Church and the abuses of the clergy, especially the granting of indulgences. . . . Hus's death caused outrage in Bohemia. His followers adopted the name of Hussites and when in 1419, Sigismund inherited the Bohemian crown from his brother, a long and bitter war broke out. . . . By an agreement made in 1436, they won control of the church in Bohemia." [1001 Days] "Hoping to simultaneously recover Bohemia, corral Italy, and solve the embarrassment of the triple papacy, Sigismund used his new authority as king of Germany to propose an international church council. He needed only one pope to sign off on the idea, and John XXIII agreed; most likely, he expected that the council would depose his two papal rivals. . . . Nearly four hundred high-ranking clergy were present . . . But they were outnumbered by university leaders, scholars, and ambassadors . . . The council had two major problems to address--the spread of Wycliffe's heresies and the scandal of the three popes--and both were as much academic and political puzzles as theological dilemmas."