If I can ask a naive question...pre-schism; who used the Western Rite? Of those people living under their respective Patriarchs, was it only the Roman Patriarchate and their people who used the rite? Or had it ever been used in any of the other patriarchates?
Actually, its more correct to speak of Western Rites. At the earliest stage of liturgical development, the liturgies in use were the Liturgy of St. James in Palestine and Syria, the Liturgy of St. Mark in Egypt and North Africa, the Liturgy of St. Peter in Rome, and the Liturgy of St. Paul (or the Liturgy of Ephesus) which was used in Asia Minor, and then was spread to Gaul, Spain, and the Celtic lands.
When Asia Minor became the seat of the Byzantine Empire, it began the process of the formation of the Imperial liturgy, which ultimately took the form of the Byzantine Rite as we know it today in the Liturgy of St. Basil the Great and the Liturgy of St. John Chrysostom.
In the West, the Roman Rite was codified by St. Gregory the Dialogist (Pope St. Gregory the Great) c. 600 A.D., and remained substantially unchanged other than in rubrics until Vatican II. At the same time, however, the Liturgy of Ephesus developed into discrete rites, specifically the Celtic Rite, the Gallican Rite, and the Mozarabic Rite (which was used in Spain). As North Africa became increasingly Latinized in terms of language, and closely allied with Rome, its Liturgy came heavily under the influence of that of Rome. When Charlemagne formed the Holy Roman Empire and added territory in Western Europe, he also propagated the Roman Rite, and forced it on the other lands, such that the Gallican and Mozarabic Rites largely died out (though the Mozarabic is still used in Toledo, Spain). One of the two Western Rite liturgies in use in the AOCA today is this Liturgy of St. Gregory.
In Britain, the Celtic Rite was joined by an Anglo-Saxon Rite, with a heavy degree of cross-pollination, and by the Roman Rite via St. Augustine of Canterbury. This remained an independent rite, however, until the time of William the Conqueror shortly after the Schism, when the Roman Rite was enforced on the whole nation. In the Anglican communion over the years, there have been a number of movements to try to recover the older Liturgies, a prime example being the Pamphleteers, which movement resulted in our having ANF and NPNF, etc. in English. One such movement, the Non-Jurors in the 18th Century, actually reassembled such an Anglican Rite, and were in talks for some time with Czar Peter the Great to become an Orthodox Church. Though those negotiations fell through, there work remained, and became the basis for the Liturgy of St. Tikhon, which the other Western Rite now in use in the AOCA. Its named for St. Tikhon because it was codified and approved for use through the work of St. Raphael of Brooklyn under the authority and with the approval of St. Tikhon while he was Patriarch of Moscow.
That's a thumbnail. The Occidentalis blog I linked to earlier has a lot more detail, especially about the Western Rite in Europe.