A series of arson attacks on schools and the bombing of Chinese shrines and a hotel in Thailand's Muslim south this week are another bitter reminder that more than a century of Thai nation-building is being sorely tested.
Thais refer to most of the country's 10 million Muslims (out of a population of 60 million) as khaek or, roughly, "guests". This in a country that has absorbed millions of Chinese, many of whom still carry a hint of a Chinese name.
And so this week, in the terrorism-dominated atmosphere of the post-Bali bombings, talk immediately turned to Islamic radicals despite Thai Prime Minister Thaksin Shinawatra insisting the attacks in the south were the "cowardly work of thugs who want to protect their drug rackets. This is mafia work, nothing more".
History lies heavy on a region where both insurgents and local gangsters have been able to move with unusual freedom in the gap between an "alien" administration and a population that prizes its separate, Muslim ways.
It is just conceivable that the ancient Muslim state of Pattani, including the five southernmost provinces, were saved for Thailand by the atomic bombs that were dropped on Japan in 1945.
When the British military thought it still might have to fight its way south into what was then called Malaya, it toyed with the idea of moving the border north - to protect Malaya's "back door" (Japan invaded Malaya via the Pattani coast in 1941) and to punish Thailand for siding with Japan.
Muslim nationalists such as Tengku Mahmud Mahyiddeen, son of the last raja of Pattani, urged the British to do just that. He and many other Muslims had been disturbed by the bossy ways of Bangkok - at its most chauvinist in the mid-20th century - that at best treated Islam as a regrettable, but passing phase.
In 1939, Siam was renamed Thailand to underline the oneness of an alleged ethnic "Tai" nation (the huge Chinese population had already been made to adopt Thai names) bound by Buddhism, racial identity and reverence for the monarch.
The atomic bomb, and American desire to foster an anti-communist client, may have killed any notion of moving the border north, but in Pattani itself, the uncertainty lingered.
"Give us back our race as Malays and our religion as Islam," said local leaders in an appeal to the outside world in 1948.
In the decades that followed, there were repeated complaints that the Thai authorities were brutal, had neglected the region so that it was "condemned to backwardness", had been attempting to suppress the local yawi Malay dialect and were trying to stop Muslims practising their faith.
Par for the centralising-state course perhaps, but the deep emotional conviction in the south that the 1909 border agreement between Siam and Britain was a colonial "accident" has bedeviled Thai attempts to absorb the south into a famously conformist state.
Insurgent groups which handed down folk memories of a Pattani "golden era" are less active than a generation ago, as hopes - and perhaps the desire - for political autonomy or linkage with Malaysia have faded.
Yet any visitor can see that a lot of truth remains in the assertion that "the Pattani Malays have . . . attempted to live within their own world as if the Thai state did not exist", in the words of historian Clive Christie.
Southern Muslims refer to themselves as "Thai" - but in Malay. Even in the south's cosmopolitan trading city of Hat Yai, it is often easier to get the New Straits Times than the Bangkok Post. Despite decades of Thai-language schooling, most people in the four majority-Muslim provinces - Yala, Pattani, Narathiwat and Satun - speak yawi.
And these are not superficial differences. In a quiet village outside Pattani dominated by a palm-fringed Mosque, the women are scarfed and shy, the men serious and helpful. But there is hardly a spark of that sometimes frisky humour, that casual curiosity of ordinary Thais.
The men shrug and smile gently as they offer careful directions and a superbly accurate hand-drawn map to the next town.
There is another difference in southern Thailand: someone keeps killing policemen, sometimes a schoolteacher or minor official.
Between late last year and this summer, 21 policemen were assassinated in the deep south. This week's torching of half a dozen schools and bombings are hardly rare.
"The government wants to say this is gangsterism, but for me, the key is Muslim organisation - terrorist organisation. You can't really explain it otherwise," said retired general Kitti Ratanachaya, a southern army commander of three decades.
"Killing officials helps them control the villages. The terror may suit some corrupt Thais, but if this was in any other region it would have been suppressed by now."
The general and most analysts say hard-core guerillas probably number no more than 100.
A Thai court recently handed life sentences to three members of the Pattani United Liberation Organisation for bombings and ambushes in the early 1980s. The police have not even named a suspect in the case of the police killings.
It is undoubtedly true that most Muslims in the south consider Thailand their home - but by choice and designation, they remain, in Thai terms, eccentric cousins.