Complex sentence: When the Siamese conquered parts of the declining Khmer Empire, the Khmer literary legacy was mostly absorbed by the Thai culture in these areas and in what we now know as Cambodia, it was stored in pagodas across the country.
Split into simpler sentences: When the Siamese conquered parts of the declining Khmer Empire, the Khmer literary legacy was mostly absorbed by the Thai culture. In what we now know as Cambodia, the literature was stored in pagodas across the country.