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mid-14th century CEReputable source · 2 sourcesWell documented

The Rising Kingdom of Ayutthaya Begins Raiding Khmer Territory

Thai migrants who once served as Khmer mercenaries build their own kingdom and turn on their former employer

On the timeline · around mid-14th century CE · Decline, the Fall of Angkor, and the Long TwilightCrisis and the Reign of Jayavarman VIIDecline, the Fall of Angkor, and the Long TwilightThe Rising Kingdom of Ayutthaya Begins Raiding Khmer Territory1250130013501400145015001550

Quick facts

Rising power
Kingdom of Ayutthaya (Siam)
Origin
Thai migrants, originally Khmer mercenaries and settlers
First Angkor conquest
1353 (briefly; Khmer regained control)

What happened

Thai-speaking peoples had migrated south from the Yunnan region for generations, first appearing in Khmer records as hired mercenaries before settling as farmers in the empire's marginal borderlands, according to World History Encyclopedia. Migration accelerated once Mongol campaigns disrupted southern China and intensified further after the Mongols conquered Yunnan in 1253. These Thai populations eventually built independent kingdoms of their own, most significantly Ayutthaya, and as those kingdoms grew stronger through the 14th century they began attacking and annexing Khmer territory rather than serving it. The National Library of Australia notes these incursions disrupted trade and undermined the safety of the empire's borders, and Angkor was briefly conquered by Thai forces as early as 1353, though the Khmer regained control afterward.

Why it matters

The empire's most persistent external threat in its final century came from a population it had itself recruited and settled generations earlier, a reminder that Ayutthaya's rise was not a sudden invasion from outside but the culmination of a long internal migration the Khmer state had allowed and even encouraged.

How we know

The Thai migration and the shift from mercenary service to independent kingdom-building is reconstructed from Khmer inscriptions recording Thai names and roles in the imperial administration, alongside Thai chronicle traditions describing Ayutthaya's own founding and expansion.

Sources

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Part of a timelineThe Khmer Empire28 events · How a trading kingdom on the Mekong became a temple-building empire that vanished into the jungleView all →
The Rising Kingdom of Ayutthaya Begins Raiding Khmer Territory · The Khmer Empire · SourcedStory