The Great Western Schism (1378 – 1415) should not be confused with the Great Schism of 1054, which was the separation of the Roman Catholic Church and the Eastern Orthodox Church (see this article). This schism was a temporary one where there were two popes.
The Italian Pope Urban VI was appointed in 1378. He was well known for his even temperament. However, when he was elected he became slightly erratic and would strike clergy and papal officers for no apparent reason. This strange behavior led the Cardinals to elect a second pope, Clement VII.
Pope Clement VII was French. But, when he came to take up the office of pope, Urban would not resign. So, Clement moved to Avignon, France and Urban stayed in Rome, Italy. Thus the Great Western Schism began—a temporary separation of France and allies from Italy and their allies.
The end of this absurd Western Schism came with the Council of Constance (1414 – 1418). In order to solve the issue a third pope was elected in 1415, Pope Martin V. However, it was not until 1418 that Urban and Clement resigned from office and the Great Western Schism came to an end.