Excerpts from Books and Wikipedia
"After three years of deliberation, on November 11, 1417, the council of Constance finally elected a new pope, a Roman called Oddone Colonna, who took the papal name of Martin V, after the saint whole feast day it was. The Papal Schism (also known as the Great Schism of Western Schism) had run on for forty years and brought the papacy into ever deepening disrepute. Since 1409 there had been three papal claimants, each with his own college of cardinals, curia, and followers: John XXIII, backed chiefly by the Germans; the Avignon pope Benedict XIII, whose support dwindled to Scotland, Sicily, Aragon, and Castile; and the Roman pope Gregory XII. In a fresh attempt to end the scandal Emperor Sigismund put pressure on John XXIII to convene a general council of the Church at Constance in southwest Germany, which opened in November 1414." [1001 Days]