A brief article about the Seven Churches which are belived to established by St. Thomas and the divisions exist between different denominations of Syrian Christians or St. Thomas Christians.
1. Seven Churches established by St. Thomas
In Kerala we have strong traditions about seven locations where churches or christian communities were established by Apostle St. Thomas himself. Six of these seven churches are very near the sea or a backwater.
Unfortunately nothing much perhaps remains or could be precisely deciphered today of the churches at Kodungallur, Chayal / Nilakkal, or Quilon. While St. Thomas himself had a share in the re-erection of the Cross at Niranam - the Cross that was thrown into the river at Thrikkapileswaram, the Kokkamangalam Cross thrown into the backwaters was re-erected by a local christian at Pallippuram.
Hence only three of the original seven churches viz the Parur church in the Syro-Malabar Archdiocese of Ernakulam, the Palayur church in the Syro-Malabar Archdiocese of Trichur, and the Niranam church under the Orthodox Syrian Church (Devalokam Aramana) could claim a continuous existence from the time of their establishment by the Apostle in the middle of the first century after Christ. 
There are traditions about half church. The church just with the Cross or Sleeba is called Half Church. The main contenders for half church are Malayattor and Thiruvithancode. Tradition associates that on the way to Mylapoor St Thomas installed cross at Malayattor.
The Thiruvithancode tradition associates the installation of cross by St Thomas on the way to China. There are local traditions at Aruvithura and Mylakombu, two old centers of Christianity in Kerala about St Thomas installing cross there.
2. Divisions among St.Thomas Christians
Despite their geographic isolation, the Church of St Thomas Christians retained the Chaldean liturgy and Syriac language and maintained fraternal ties with the Babylonian (Baghdad) patriarchate; their devotional practices also included Hindu religious symbolism.
Several mass migrations of Syrian Christians to the Malabar Coast (9th century) also strengthened their ties with the Middle East.
Direct contact with Rome was infrequent until the arrival of Portuguese missionaries in the early 16th century. The Portuguese, after initial professions of friendship, started a concerted effort to subject the Church of St Thomas Christians to their obedience, replacing the Chaldean bishops with Portuguese ones and Latinizing the Malabar liturgy.
Portuguese started a Latin diocese in Goa (1534) and another at Cochin (1558) in the hope of bringing the Thomas Christians under their jurisdiction. In a Goan Synod held in 1585 it was decided to introduce the Latin liturgy and practices among the Thomas Christians.
The Portuguese refused to accept the legitimate authority of the Indian hierarchy and its relation with the East Syrians and at a synod held in Diamper ( Synod of Diamper ) in 1599, the Portuguese Archbishop of Goa imposed a large number of Latinizations.
The Syrian Chaldean patriarch was then removed from jurisdiction in India and replaced by a Portuguese bishop. The Syrian liturgy of Addai and Mari was “purified from error” and Latin vestments, rituals, and customs were introduced to replace the ancient Syrian traditions They latinized the liturgy and introduced the Inquisition.
The Portuguese succeeded in appointing a Latin bishop to govern the Thomas Christians. The Portuguese padroado was extended over them. From 1599 up to 1896 these Christians were under the Latin Bishops who were appointed either by the Portuguese Padroado or by the Roman Congregation of Propaganda Fide. Every attempt to resist the latinization process was branded by them heretical.
Under the indigenous leader, Archdeacon, the Thomas Christians resisted, but the result was disastrous.The first solemn protest took place in 1653 with the Koonan Cross Oath. Under the leadership of Archdeacon Thoma, a major section of the Thomas Christians publicly took an oath that they would not obey the Portuguese bishops and the Jesuit fathers.
Consequently, the majority of the Christians of St. Thomas left Portuguese rule in 1653, swearing never to submit to Portuguese domination. When the news of the rebellion reached Rome, Pope Alexander VII sent the Syrian bishop Sebastiani at the head of a Carmelite delegation to Malabar in 1661 and established a hierarchy of Chaldean rite under Rome. 
By 1662 majority of the Christians of St. Thomas had returned to Catholic fold (the Syro-Malabar); the rest joined the Syrian Jacobite (Monophysite) Church in 1665.
In 1665 an Antiochean bishop Mar Gregorios arrived in a Dutch ship and the dissident group under the leadership of the Archdeacon welcomed him. This was the starting point of division among the Syrian Christians in Kerala who till then were one Church.
Though most of the Thomas Christians gradually relented in their strong opposition to the Western control, the arrival of the Bishop Mar Gregory of the Syriac Orthodox Church in 1665 marked the beginning of a formal schism among the Thomas Christians.
Those who accepted the West Syrian theological and liturgical tradition of Mar Gregory became known as Jacobites (Malankara Jacobite Syrian Church (Syriac Orthodox Church). The Jacobites adopted the Western Syrian language and Antiochene liturgy in their church.
Those who continued with East Syrian theological and liturgical tradition are known as Syro Malabar Church in communion with the Catholic Church. The Syro Malabar Church kept the East Syrian liturgy but increasingly latinized it. The Holy Qurbana was celebrated in Syriac language till 1962 July.3.
St Thomas Christians by this process got divided in to East Syrians and West Syrians in liturgy.
In 1772 West Syrian’s under the leadership of Kattumangattu Abraham Mar Koorilose, Metropolitan of Malankara formed the Malabar Independent Syrian Church (Thozhiyur Sabha).
In 1874 a section of East Syrians from Thrissur came in to communion with Catholicos Patriarch of the Church of the East in Qochanis ( Melus / Rokkos schism in Syro Malabar ). They follow the East Syrian tradition and are known as Chaldean Syrian Church.
In 1845, exposure to the doctrines of the Church of England inspired a reform movement led by Abraham Malpan in the West Syrian community. This led to the formation of the Mar Thoma Church.
However, in 1912 there was another split in the West Syrian community when a section declared itself an autocephalous church and announced the re-establishment of the ancient Catholicosate of the East in India. This was not accepted by those who remained loyal to the Syrian Patriarch. The two sides were reconciled in 1958 but again differences developed in 1975.
Today the West Syrian community is divided in to Malankara Orthodox Syrian Church (in Oriental Orthodox Communion), Jacobite Syriac Orthodox Church (in Oriental Orthodox Communion)
In 1926 a section of West Syrians under the leadership of Mar Ivanios came in to communion with Catholic Church retaining all of the Church’s rites, Liturgy, and autonomy. They are known as Syro-Malankara Catholic Church.
Portuguese caused the division among Nasrani’s. Dutch and Bristish colonialists also added oil to the divisions of Nasrani Syrian Christians for their own benefits.
From the days of the unfortunate division among the St. Thomas Christians in 1653, there have been attempts at reconciliation between the Churches.
But due to the negative attitude of the western missionaries, who were generally afraid of losing their authority in Malabar and sometimes the scrupulous attitudes of the Orthodox Church leadership, these attempts were mostly futile.
Joseph Cariattil, Thomas Paremmakkal, Mar Thoma IV, V, VI (Dionysius I), Nidhiry Mani Kathanar, Thachil Mathoo Tharakan, and Mar Ivanios are some of the great souls who tried for re unification and unity among various Nasrani denominations.
Though a complete reunification reviving the old traditions looks a distant possibility, there are many people among the communities who shares this vision.
 Articles of Prof. George Menanchery
 Encyclopaedia Britannica