What are the origins of the LTTE and the related issues of the Tamil people in Sri Lanka?

This is a very long and complicated question that is still, even following the defeat of the LTTE in 2009, a sensitive topic. While it pushes up against the 20 year rule, I will do my best to stick to the conflict before 1997, though it will limit the discussion of the Tamil Tigers and the Śrī Lankān government's war crimes as well as the ongoing issues following that defeat. If you would like to learn more about that, I'd be happy (well, not happy per se, it is a bit of a somber topic) to follow up in a PM or you are welcome to post a question over at r/asksocialscience or /r/ask_politics (though neither are as thorough as this one.

Sorry this took so long, in my defense, it is something like 30 pages and by far my longest post here. I think I went a little overboard in the beginning and eventually ended up burining out towards the end, sorry for that. I will give more clarification later on and probably expand more on the role of international funding for the LTTE and the role of India and Dravidian Nationalism as well as war crimes committed by the Śrī Lankan government, but right now it is 2:15 and I've been working on this since it was asked.

#Part 1: The Ancient History and Historical Justifications for the Conflict

The Tamil people have been present in Śrī Lankā, especially the north where it is not far from Tamil Nadu for a very long time, though not as long as some would claim. The original inhabitants appeared about 37,000 years ago and left behind caves. These were anatomically modern humans, likely from the coasts of India who migrated there by boat. They are likely the ancestors of the Vedda people of Śrī Lankā, of whom there are very few left.

The people who now dominate Śrī Lankā are the Sinhalese, who trace there ancestry to the legendary exiled Prince Vijaya and his retinue of 700 advisors. According to the legendary epic, the Mahāvaṃsa (Pāli: Great Chronicle), they were exiled for general "evil deeds". In any case the chronicle places them as being from present day Bengal and having obtained Pandya brides, which is confirmed by Genetic evidence.

The Tamils (specifically the Pandyas) may have had settlements on the island before the Sinhalese people (or rather the people who would become Sinhalese), but there is not archeological or textual evidence for it. The first evidence of Tamil presence occurs in the Mahāvaṃsa, backed up by inscriptions, slightly before the reign of Aśoka the Great in India. King Devānampriya Tissa, not to be confused with Aśoka who called himself Devānampriya, appeared to rule over a mixed kingdom, though he himself converted to Buddhism and patronized it. Years later, the Dravidio-Tamil king Eḷāra held control of the northern plains of Śrī Lankā after having taken over the Anurādhapura kingdom founded by the Vijaya dynasty, and the Sinhalese in the the south led by Duṭṭagāmaṇī of Rohaṇa. While the Mahāvaṃsa paints this conflict as one of the Buddhist Sinhalese people against the Brahminical Tamil usurpers, the evidence shows that it was far more complicated than just that.

The Sinhalese and Śrī Lankān Tamils both mixed quite a bit during the centuries and they both led mixed kingdoms. During the time of Eḷāra both kingdoms had a significant population of Tamils and Sinhalese. Thus the war was neither a holy war or a racial war like some modern commentators (and indeed the Sinhalese who wrote the document) have claimed. Nonetheless, the war established Sinhalese dominance over the whole island, something that would be essentially unchecked for eight centuries.

Eight centuries later, Śrī Lankā was fractured into two rival kingdoms, both of whom relied heavily on Tamil mercenaries and generals leading to a powerful Tamil aristocracy. In 642, Māhavamma took control and curbed the power of the rich Tamil aristocracy, though he still kept a retinue of Tamil mercenaries. However, Śrī Lankā was facing increasing military and economic pressure from the three kingdoms of South India, the Coḷas, Pāṇḍyas, and Pallavas.

These kingdoms were strongly militant and very Hindu. The Pāṇḍyas were the first to invade and held the northern coast, but were beaten back by the Sinhalese. However, at this time the Coḷas took control of Pallavan territory and the Sinhalese half-heartedly supported the Pāṇḍyan efforts to beat back the Coḷas, but were unsuccessful and eventually, the Coḷas took control of Śrī Lankā ending over 1 thousand years of Sinhalese rule.

The Tamil rule over Śrī Lankā was actually quite short, only a few years and not uncontested. However, the Coḷa's left a deep scar on the island and numerous places were never rebuilt. The Coḷas ruled over the north coast for some time and retained considerable influence over the island in terms of trade. The invasions (along with the fracturing of the saṅgha due to the arrival of Mahāyāna) nearly destroyed Buddhism in Śrī Lankā and the Sinhalese were forced to call upon the help of Pagan to restore Buddhism and regain the Pāli Canon.

Conflict between the Tamil Kingdoms (who would eventually gain independence Pāṇṣyas) from the Sinhalese Kingdoms would continue and range from violent war to a tenuous peace. However, this does not mean that relations between the Sinhalese PEOPLE and Tamil people was poor, even the relations between Buddhists and Hindus was fairly okay. In fact, during this period, there was a significant deal of syncretization between Hinduism and Buddhism, stating around this time, Hindu temples often contained Buddhist iconography and Bodhisattvas and Buddhist Temples often had Hindu Icons and Deities were worshiped.

Furthermore, the relations between various religions was comparable to those under most contemporary Indian ones with powerful elites patronizing all sects. This encouragement of religious pluralism had a strong effect upon the local populace and led to generally friendly relations and little persecution overall.

In a somewhat confusing note, many of the Sinhalese in Coḷa (and later Jaffna) Tamil territory were "Tamilicized", converting to Vaiṣṇavism and adopting Tamil language and customs while Tamils in Sinhalese territory were "Sinhalized" and doing likewise. It is not an understatement to say that nearly all Sinhalese today have mixed lineage with Tamils and all Śrī Lankān Tamils have Sinhalese blood.^3

As we can see, there has been tension since Ancient times, but that tension is often overstated and wrapped up with both Tamil or Sinhalese-Buddhist Nationalism. I also skipped over the arrival of the "Sinhalese Moors", who are the descendants of Muslim traders and represent a significant minority in Śrī Lankā, they used to get along fairly well with people, but unfortunately have found themselves disenfranchised since the beginning of the current conflict.

#Part 2: Portuguese and Dutch Rule: Suppression and Conversion

By the 16th century, Europeans had entered the scene like never before, attempting to take control of the fertile landscape and strategic location of the island. The first to do so were the Portuguese who quickly conquered the Northern and Western parts of the island but ran into difficulties maintaining a proper hold over it. The Portuguese were notorious in their conversion efforts and repression of local religions and customs, and their efforts to control Śrī Lankā were no exception making them extremely unpopular with all people on the island, Tamil and Sinhalese alike. The Sinhalese kingdom of Kandy was the first to rebel and allied themselves with Jaffna and the other powers in Śrī Lankā at the time, outside of Kotte which was a Portuguese client state. The Dutch allied themselves with Kandy in 1638 and eventually expelled the Portuguese from their stronghold in Colombo in 1656, betraying Kandy and finally the Portuguese were expelled from Ceylon in 1658.

The Portuguese ethnic policy was one fierce suppression. Ethnic and religious pluralism had no place for the Portuguese. All powerful or even administrative positions in Portuguese Ceylon were held by Roman Catholics. The Portuguese were indiscriminately iconoclastic, destroying Buddhist and Hindu holy sites alike and putting devotees, monks, and clerics of all sects to the sword. In addition, social aspects that the Portuguese found distasteful were removed but the ones they found helpful, such as caste, were increased. This lead to a sharper marker between the Sinhalese and Tamils.

In any case, the Dutch took control over the North and South of Śrī Lankā and quickly established a treaty with the Kandyans to limit tensions and establish an economic presence with Kandy. Dutch ethic policy was similar to Portuguese, but more established and evolved. While corruption was greater in Dutch Ceylon, with wealthy Dutch stealing land, the overall structure of the government was somehow more functional. Religious policy was somewhat more subdued than the Portuguese and while the Dutch were hostile to non-Calvinist Christianity (they persecuted the Roman Christians) they weren't as fervent about it allowing Hindu Tamils to own land and did not go out of their way to destroy temples. Indeed their hostility toward Catholicism hampered their own missionary efforts and turned many back to Buddhism and Hinduism, though their persecution of the Muslim population was hardly better than the Portuguese. Notably, the Dutch used a different law code for the Sinhalese, Tamils, and Moors, though they used their own for the Sinhalese.