Conversation so far:
What is the Mekong Delta?
In the 17th century a weakened Khmer state left the Mekong Delta poorly administered after repeated warfare with Siam.
What did Khmer do?
control of the area grew increasingly tenuous while increasing waves of Vietnamese settlers to the Delta isolated the Khmer of the Mekong Delta from the Cambodian kingdom.

Question: When did Vietnam absorb it?
Self-contained rewrite: When did Vietnam absorb the Mekong Delta?