During his reign, the Lam Sơn uprising's Vietnamese leader Lê Lợi requested that Lan Kham Deng send some troops to help the Vietnamese fight off the Chinese, who were suppressing them during the rebellion. Lan Kham Deng sent thousands Laotian of troops to aid the Vietnamese, but for some reason, the armies of Lan Xang turned on the Vietnamese and fought on China's side.
Eventually, Vietnam defeated China. By that time, Lan Xang's relations with Vietnam were deteriorated and it led to the revenge of Vietnamese emperor Lê Thánh Tông in Đại Việt–Lan Xang War (1479–1484)
. The war with Vietnam caused chaos in Lan Xang followed by many attempts by royals to seize the throne.
Lan Kham Deng died in 1428 at the age of 53. He had ruled for 12 years.