Funan leaned on its vassal Chenla — the vassal grew strong and swallowed its overlord

Funan was the great maritime kingdom of the lower Mekong — the entrepôt between China and the Indian Ocean — and for centuries it ruled through vassals. Chenla, an inland kingdom upstream, was one of them: the Chinese dynastic histories that record both states describe Chenla as a dependency of Funan.

The Sui histories note that Chenla had been growing stronger since the grandfather of its king Citrasena; under Citrasena himself, around the turn of the seventh century, it annexed Funan and took its place. The Tang histories carry the story on: in the early Zhenguan era, under king Ishanavarman, Chenla 'annexed Funan and held its territory'. After the annexation it is Chenla, not Funan, that the Chinese records describe.

No chronicle records a moment of decision at the Funan court — that is the point. The shift happened inside a relationship Funan treated as fixed: the vassal grew strong by degrees, and the overlord discovered the new balance of power only when it was announced by annexation.