Is Christianity a Western Religion? Consider the Eastern Orthodox Church.
Christians in the West often forget about the Eastern Orthodox Church, a schism with the Roman Catholic Church that began around 1054 and spread throughout Greece, Turkey, The Middle-East, and Russia (whereas the Catholic Church spread to the West).
This branch of Christendom is no less legitimate than Catholicism or Protestantism when accounting for the mere presence of Christianity across the globe. Although not as prevalent in what we often consider the “East” (India, Asia, the isles), this church’s adherents are East of what we call the West; it is deeply rooted in the East and Middle-East.
Being the second largest Christian denomination in the world, there are almost as many Orthodox adherents today as there are Roman Catholic. The majority of religious people from Belarus, Moldova, Serbia, Jordan, Lebanon, and Russia, for example, will claim to be Eastern Orthodox. There are also many adherents on all seven continents.
The Eastern Orthodox’s focus on the divinity of the trinity outnumbers some Western, Protestant denominations, some of whom deny the divinity of Father, Son, and Holy Ghost. This Church also differs significantly from most Western denominations in its belief about the fall of man, the nature of atonement, the concept of free will, the existence of purgatory, and the end of days.
During the Crusades, the Eastern Orthodox Church was even persecuted by the Roman Catholic Church. The West persecuted this Eastern denomination.
The Eastern Orthodox Church and its presence in the East is for us in the West a reminder of how we put blinders up as we see the world. We often forget how our legacy is often only part of a greater legacy, and we fail to define the world by anything other than whether something is part of our presence or something not part of our presence as global Westerners.
[A note on the name “Eastern”: While the Eastern Orthodox Church retains the name “Eastern,” this does not make it representative of the cultures of Asia so much as a representation of Christianity as practiced by those who split Eastward from the Roman Catholic Church in a thousand years ago. Geographically, one may call the Eastern Orthodox Church more Middle-Eastern than Eastern. But as we have seen, and will continue to see, this talk merely ends up being mostly about geography and politics anyway, and it has been argued by many (mostly Protestant) that neither Catholicism nor Eastern Orthodoxy reflects the practices of Christianity as accurately or as primitively as was practiced and/or is still practiced across the world by other groups practicing Christianity.]
Your first and last paragraph talk about the origins of the Catholic and Orthodox Churches. If one church split from the other, then the Catholic Church split from the Eastern Orthodox Church, not the other way around. (This is debatable, especially by the Catholic Church.)