The two theological questions at play in the long drawn out Great Schism (1054 to 1472), also called the East-West schism or the Eastern Schism, were the wording of the Nicene Creed in relation to the filioque clause identifying from whence the Holy Spirit proceeds and azyme bread. The Eastern Church called the Western Church heretical because they added the clause that specifies the Holy Spirit proceeds from "the Father and the Son" and because they switched to unleavened bread.
The Second Ecumenical Council of 381 specified that the Holy Spirit "proceeds from the Father." This is the wording that the Greek speaking Eastern sector of the Church held to while the Latin speaking Western sector added "and the son": the Holy Spirit proceeds "from the Father and the Son."
The ancient traditional way of serving the Eucharist was to use leavened bread. This is what the Greek Eastern sector continued to hold to. The Latin Western sector switched to azme, or unleavened bread that is like Jewish unleavened bread. They switched sometime after they had excommunicated and schismed Caerularius. These are the two theological issues involved in the Great Schism, which was additionally affect by the complete Latinization of the Latin speaking Western sector and the near-complete Hellenization of the Greek speaking Eastern sector.
Thanks! It helped heaps :)