Well, finals are over, so I will add my view here. Forgive me if this does not come out right; I really don't mean any offence.
I would be remiss if I did not thank Mikho for his compliment at the outset. Mikho and I have exchanged emails in the past regarding the situation in India, and it has always been (for me, at least) a very rewarding experience to converse with him on a friend-to-friend basis, and hear his views as I try and formulate my own view of things as they are.
The split originated because of Indian nationalism in the early 20th century. A very small minority within the SOC in India sought to distance themselves from any foreign, and as a result, tried to break the entire SOC in India from the rest of the SOC. This movement was not the will of the majority of the SOC in India, so rather than stand down and submit to their bishops, this new movement arose. It continued to gain favor along with the tide of Hindu nationalism (India had been under foreign occupation for several hundred years).
Church historians for the Syrian Orthodox Church see it as Mikho writes here. Church historians for the Indian Orthodox Church, as you can imagine, see it a bit differently. I've never been a "My Church: Right or Wrong" person, and so I can admit that, from my limited knowledge of the events in question, the origins of the IOC were not immaculate (although I will not go so far as to say they were thoroughly rotten or treacherous).
From what I have been able to gather (and it's been a while since I've seen my sources because, thankfully, I haven't had to do this in a while), the Church in India around the nineteenth century was governed by Syrian (read: Middle Eastern) bishops, although the priests and deacons were indigenous. There was a clamour for Indian bishops; certainly, this request is a reasonable and understandable one. The Indian Church wanted some say in who was selected to be a bishop, but this was denied by the Patriarchate, which chose and consecrated someone that the Indian clergy specifically asked not to be consecrated because they knew who he was and what he was up to.
He, along with some others, were preparing to found the Mar Thoma Syrian Church, a "reformed" offshoot of the Orthodox Church, with a reformed, stripped down Syrian Liturgy that could only be classified as a "Novus Ordo" type service and Protestantised doctrines. Ordaining a man as bishop who is going to start such a group is a mistake. Nevertheless, it was done by the Patriarchate (I think the bishop in question was Mathew Mar Athanasios) against the wishes of the Indian clergy who knew this man's intent. He promptly left the Orthodox Church, starting his group: the Liturgy was translated (in a bastardised form) into Malayalam, was very much simplified, and Protestant doctrine began to be promoted. Because the Liturgy was in the vernacular for the first time, many people were attracted, and through this fell for the Protestant doctrines as well, with the full support of the Church Mission Society of the Anglican Church (I think that's what they were called).
The situation didn't get much better, and so in 1912, Patriarch Abdul Messiah came to India and consecrated Vattasheril Mar Dionysios as Catholicos of the East. This Patriarch was formerly Patriarch of Antioch, but was ousted from the throne and replaced, if I'm not mistaken, by Patriarch Abdullah, who I've heard was a convert from the Roman Catholic Church. Why was Abdul Messiah kicked out? I've heard all sorts of different stories, depending on whom you ask, and so it is hard for me to establish whether or not his ousting was legitimate. For argument's sake, however, let us assume that he was legitimately deposed. This would make his actions in Malankara in 1912 uncanonical, and the resulting Church would be an uncanonical group.
In 1934, the new group, the Malankara Orthodox Syrian Church (or IOC, for the sake of this thread) adopted a Constitution to govern ecclesiastical affairs. This Constitution recognises the spiritual primacy of the Patriarch of Antioch, although it gives temporal authority over the administrative affairs of the Indian Church to the Metropolitan of Malankara (an office fused with that of the Catholicosate).
Around 1957, the Patriarchate of Antioch accepted the Constitution of the IOC as it was, making, to my knowledge, no changes. The two factions of the Church were reconciled, and there was peace in a united Church, recognising the spiritual primacy of His Holiness the Patriarch, and the administrative authority of His Holiness the Catholicos. The Patriarch visited India and consecrated our Catholicos (on a personal note, it was during that visit that, among other places, he offered the Holy Liturgy in my mother's parish church, and my mother and her family were communed by him).
In Addis Ababa in 1965, there was a meeting of the heads of the Oriental Orthodox Churches summoned by His Imperial Majesty, Haile Selassie of Ethiopia. The Indian Church was represented by His Holiness Moran Mar Baselios Augen I, who in the documents of that council was recognised as Catholicos of the East, Metropolitan of Malankara, and "of the ancient See of Saint Thomas".
Hence, while in 1912 you had a Church one might legitimately be suspicious of, all was reconciled by the late 1950's, making the Church in India unequivocally canonical, under the Constitution which was approved as is by the Patriarch. In 1965, we see the Oriental Orthodox Churches, gathered in council, recognising us as an independent Church (and, it goes without saying, canonical).
However, shortly after this, problems arose again, and the Church was divided. What exactly the problems were I haven't been able to figure out (much of the history is written in Malayalam, and although I know the language, I don't know it well enough to read official documents for these purposes). The basic jist of things seems to be that the Patriarch was trying to do something that was overstepping the bounds agreed to in the 1934 Constitution ratified by the Patriarchate in 1957.
Related to this, much ado is made of a Patriarchal Bull sent to our Catholicos which allegedly said that the Apostle Thomas did not possess the powers of the Episcopacy/Priesthood, although the Apostle Peter did (special mention was made of Saint Peter, IIRC). I have not read the Bull; I trust it is written in Syriac, and I have not seen a translation in either of the two languages I'm comfortable with. Nevertheless, there are people who have seen it at least in translation, and can even cite it by its number, and so I have no reason to believe that it is a lie (why would you lie about something that apparently is easy enough to confirm one way or the other?). This was seen as an attack on the authority of the Metropolitan of Malankara, who sits "on the ancient See of Saint Thomas", even if this See cannot definitely be linked to a particular city. Furthermore, it was viewed as somewhat heretical to deny these things of the Apostle Thomas. It also flies in the face of longstanding tradition, among Indians and Copts, that the Apostle, before his glorious martyrdom, consecrated at least one bishop, in addition to priests and possibly deacons.
All of these things came together, and Catholicos Augen excommunicated the Patriarch (this is what I hear anyway...I can't be certain, but I'm pretty sure it was a personal excommunication) for these things. This excommunication was returned, and there were two Churches, and at some point the Syrian Patriarch consecrated a Catholicos for the faction faithful to him. With little change, this has sadly remained the case to this day.
I really didn't intend to write this much merely on the first quotation, but I got carried away. At any rate, the original quote dealt with how the IOC gained steam with the rise of Hindu nationalism. I do not deny that, among some, perhaps among a good number, nationalistic concerns are a part of this. What I do deny, however, is that this is the only thing. What I wrote before still stands: in my considered opinion as the person here most immersed in the situation, nationalism is low on the list of reasons why this is all going on. Mikho speaks of India being under foreign occupation for several hundred years; I don't see what that has to do with the Malankara Church, however, since, unless I am grossly mistaken, the entirety of (present day) Kerala was under the governance of native Princes, and not under the British Raj.
To be continued...