Slavery existed in Kerala in early 19th century, Christian missionaries helped abolish it

A keen observer of history, culture and politics, Bhaskar Sur, in a Facebook post, has brought to light an unusual fact: Existence of slavery in India at a time slavery ruled the roost in America and Europe. Even as providing link to a short article published in a little known site “Nalloor Post”, he says, “There are many post-colonial historians who have dwelt exhaustively on the Trans-Atlantic slavery and its relation to capitalism. While we should admire the quality of the scholarship, we cannot help feeling that it is history writing with an agenda.”
According to Sur, “For instance, they usually bypass or elide such disturbing questions regarding the Arab role in this trade which, as we now know, was considerable. There were different dehumanizing forms of slavery in the pre-colonial India. They were abolished largely owing to the efforts of the missionaries (agents of imperialism in the post-colonial narrative) and by the British intervention.”
He produces an article on the prevalence of slavery in the Trivancore-Cochin state, which is now present-day Kerala. “What is most disturbing is the percentage of the slave population which was higher than the black slaves in Antebellum America.”
Reproduced is the article published in “Nalloor Post” titled “8 March 1835, Freedom for Kerala Slaves. (Munro Island – Travancore)”:

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Slavery was a social evil which prevailed all over the world including what is now the state of Kerala in India. According to the 1836 census there were 164,864 slaves in Travancore vis-à-vis a total civilian population of 12,80,668.
Slaves were treated like animals and the cost of one slave was that of an ox, cost of an ox was 5 (big para) measures of Paddy or Rs. 10/- only. Slaves were chained and sold like animals in markets.
Kottayam, Changanasserry, Thirunakkara, Alleppey, Kayamkulam, Kollam, Attingal, Chirayinkizh, Kaniyapuram, Pettah and Kovalam were the notorious slave trade markets of the time. Churches in Cochin were used as godowns for the slaves except for Sundays. Slaves were exported out of the kingdom. There was no one to speak on behalf of these unfortunate people.
With the arrival and the teachings of the CMS (Church Missionary Society) missionaries, people became aware of this social evil. In 1819, Munro Island was given to the missionaries, by the then Travancore Government along with the slaves residing there on the Island. Munro Island is located at the confluence of Ashtamudi Lake and the Kallada River, in Kollam district, Kerala, India.
In 1833, England passed the Slavery Abolition Law. CMS missionaries, Benjamin Bailey and Joseph Peet made a historic declaration on 8th March 1835, giving freedom to the slaves in Munro Island.
The declaration read as follows:
“We the undersigned, acting as trustees of Munro Island, do hereby declare that… who has hitherto been a slave of the soil, is from this time liberated by us and made a free man and that his wife and offspring are wholly and forever free and are regarded by us only as hired servants and that no one has any right to bring them into servitude again. At the same time we declare that we do not consider ourselves as released from any claim which he or his wife or offspring may have upon us according to custom, privilege or law in consequence of their having been slaves.”
8 March 5. Sd/- Benj Bailey Sd/- Josh Peet. 
In 1847, Uthram Thirunal Marthanda Varma became the King of Travancore. The same year CMS missionaries submitted a memorandum to the King requesting him to stop the slavery in Travancore. In 1853, by royal declaration slavery was abolished in Travancore forever. In 1864, the Kingdom of Cochin also made a similar declaration abolishing slavery.