Short answers, pulled from the story.
The 23 Eastern Catholic Churches originated when groups within ancient churches returned to full communion with the Bishop of Rome. The Council of Florence between 1438 and 1445 marked a period where several eastern churches associated themselves with Rome while maintaining their own liturgical heritage.
The Great Schism of 1054 began when Patriarch Michael I Cerularius and Papal Legate Humbert of Silva Candida issued mutual excommunications between Constantinople and Rome. These excommunications remained unrevoked until 1965, yet hostility had already taken root by the 12th and 13th centuries.
The five historic liturgical traditions include the Alexandrian Rite, the Armenian Rite, the Byzantine Rite, the East Syriac Rite, and the West Syriac Rite. All five rites are represented within the current Eastern Catholic liturgy as defined by the Church.
The 1990 Code of Canons of the Eastern Churches became the first codified body of canon law governing all Eastern Catholic Churches collectively and took effect in 1991. It serves as a framework document containing canons derived from common Eastern patrimony while each individual church maintains its own internal laws.
Eastern Catholic Churches have always allowed ordination of married men as priests and deacons, with 90% of diocesan priests being married within the Ukrainian Greek Catholic Church. Most Eastern Churches distinguish between monastic and non-monastic clergy, where bishops are normally selected from monastic clergy while many parish priests remain married.