NEW YORK, March 31 (UPI) -- U.S.-led scientists say they have found evidence suggesting changing environmental factors, including drought, can cause a civilization's collapse.
The researchers, led by Brendan Buckley of Columbia University's Lamont-Doherty Earth Observatory, say decades of drought, interspersed with intense monsoon rains, may have helped bring about the fall of Cambodia's ancient Khmer civilization at Angkor nearly 600 years ago.
The scientists reached their conclusion after conducting an analysis of tree rings -- the longest tropical tree ring record studied to date.
Historians have offered various explanations for the fall of the Angkor civilization that stretched across much of Southeast Asia between the 9th and 14th centuries. But the scientists said their new findings offer the strongest evidence yet that two severe droughts, punctuated by bouts of heavy rainfall, may have weakened the empire by shrinking water supplies for drinking and agriculture, and damaging Angkor's vast irrigation system, which was central to its economy.
The kingdom is thought to have collapsed in 1431 after a raid by Siamese from present-day Thailand.
"Angkor at that time faced a number of problems -- social, political and cultural," Buckley said. "Environmental change pushed the ancient Khmers to the limit and they weren't able to adapt. I wouldn't say climate caused the collapse, but a 30-year drought had to have had an impact."
The research appears in the Proceedings of the National Academy of Sciences.