The Western Schism was a split between factions of the Roman Catholic Church between 1378 and 1417.
During this period, more than one claimed to be the true pope.
The reasons for the split were mostly political, rather than theological. The Council of Constance (1414–1418) ended the schism when they elected Martin V as the new pope.
"Western Schism" . Catholic Encyclopedia. New York: Robert Appleton Company. 1913. Cite has empty unknown parameter: |HIDE_PARAMETER= (help)CS1 maint: discouraged parameter (link)