In his apostolic exhortation of 1994,Tertio Millennio Adveniente, John Paul II called for a confession of Catholic sins in the past, including sins against unity. "Among the sins which require a greater commitment to repentance and conversion should certainly be counted those which have been detrimental to the unity willed by God for his people."
Source: Pope John Paul II - Tertio Millennio Adveniente, 34