On January 29th, 2003 the Thai embassy in Cambodia was burned during a riot over a rumor that a Thai actress claimed Angkor Wat belonged to Thailand. Rumor or not, how did something like this happen over a claim? The problem is deep rooted in history.
Look closely at Cambodia and Thailand and you will see that the nations share very similar customs, traditions, beliefs and ways of life. It’s even more apparent in the royal customs, language, writing systems, vocabulary, literature, and dramatic arts.
In spite of having these similarities it’s surprising that relations between Thailand and Cambodia should be characterized by deep-seated “ignorance, misunderstanding, and prejudice.”
This lack of understanding is reflected in the thinking of a considerable number of educated Thais and members of the ruling class, who distinguish between the Khom and the Khmer, considering them to be two separate ethnic groups. They assert that it was the Khom, not the Khmer, who built the majestic temple complexes at Angkor Wat and Angkor Thom and who founded one of the world’s truly magnificent ancient empires. They further claim that Khmer culture, for instance its various forms of masked dance drama, is merely a “derivative” of Thai culture.
In full here.