In the early 1400s, reforming Bohemian priest, Jan Hus, denounced corruption in the Catholic Church and the institution of the papacy. The Council of Constance was convened, supposedly to arbitrate, but Hus was seized there and burned as a heretic. Open revolt now broke out amongst his followers, the Hussites, and Catholic forces were sent to subdue them at the battle of Sudomer in 1420. The Catholics were defeated and a series of crusades (1421–31) against the Hussites followed, proclaimed by successive popes. Each would fail due to the effectiveness of the Hussite generals, notably Jan Zizka and Prokop the Great. The Hussites were also battlefield innovators using the wagenburg (a circle of wagons concealing infantry, horsemen, and artillery) tactic to devastating effect against the heavily armoured cavalry. Fighting continued until 1434 when Prokop was killed by revolting Hussites, who then concluded a peace with the Catholic Church.
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