By Nopporn Wong-Anan

BANGKOK, May 14 (Reuters) - It takes more than a natural disaster to wipe out centuries of bad blood.

In Thailand, where school books and movies overflow with tales of atrocities and brutality by invading Burmese armies, the devastation wrought by Cyclone Nargis has left some people thinking Myanmar only got what it deserved.

At the official level, Bangkok has pulled out all the stops to help in the wake of the May 3 disaster, which has killed up to 100,000 people and left 1.5 million more clinging to survival in the Irrawaddy delta.

Thailand was the first country to fly in aid and some of its biggest companies were among the first to pledge donations in cash and kind. Its revered royal family also donated supplies of food, blankets, water and mosquito nets.

Its Prime Minister also tried many times to intercede on behalf of the United Nations, appealing -- in vain, it now seems -- to the generals in charge of Myanmar to throw their doors open to a massive international aid operation.

But some Thais feel that the country's ancient foe immediately to the west got what it deserved for destroying the ancient Siamese capital of Ayutthaya in 1569 and 1767.

"After all the things they have done to Thailand since ancient times, this is the karma they deserve," 'Ayutthaya' wrote in a forum on the website of the popular Manager newspaper.

According to conventional Thai history, hundreds of thousands of Burmese troops took tonnes of gold from the state coffers when they sacked Ayutthaya, 80 km (45 miles) north of Bangkok, set fire to temples and taking thousand of captive slaves.

The city was so destroyed the new Thai king had to move the capital south towards Bangkok.

"Burma is Thailand's No 1 enemy. If we want to help, send them mouldy curry or rotten eggs. The Burmese are ungrateful," 'Thai Blood' wrote on the same board.

Such views were in a small minority, outnumbered easily by sympathetic readers who directed their anger at the Myanmar military, which has ruled the country since 1962 and turned it into one of Asia's poorest countries.

But they also reflect decades of propagandist nation-building in which the former Siam's prosperity, peace and on-off democracy are contrasted directly with the misery and anarchy inside its military-ruled neighbour.

"We have been indoctrinated by a history of hatred from the media, from textbooks in elementary schools and from TV soap operas and films," said historian professor Charnvit Kasetsiri of Thammasat University in Bangkok.

The most expensive Thai movie ever made was King Naresuan, a swashbuckling 2007 epic about a 16th century Siamese monarch who liberated Ayutthaya from the evil clutches of the Burmese, single-handedly killing his opposite number in an elephant duel.

Chulalongkorn University analyst Pornpimon Trichot said the Thai government's clear desire to assist after the cyclone might help dismantle the "illusion" about its neighbour, which has reserves of raw materials and energy Bangkok would love to access. Thailand is home to 2 million Burmese migrant workers.

"As the humanitarian drive is well-received among many Thais, we are seeing the Burmese as human beings like us, not enemies," Pornpimon said. (Editing by Ed Cropley)

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