After 1431, when armies from Thailand
captured and sacked Angkor, the city was
abandoned by most of its citizens.
Some historians have considered the mass conversion to
Theravada Buddhism as having been responsible for the abandonment of Angkor, which
certainly accompanied the conversion in the 14th and 15th centuries. That
argument has been undermined by the fact that Theravada Buddhists from Thailand profited from and even accelerated the collapse by their
repeated military attacks, in which hundreds and perhaps thousands of
Cambodians were led to captivity in Thailand.
Recorded Tai attacks on Angkor occurred in
1369, 1389, and 1431, after which the Khmer capital was definitely abandoned.
There undoubtedly were other attacks as well.
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Britannica
