During the twenty-year span of Đại Việt’s fourth period of Chinese domination, the good relationship between Lan Xang and Đại Việt began to degenerate. In 1418, Lê Lợi, the son of a Vietnamese aristocrat, initiated a guerrilla war against the Ming. In 1421 during Đại Việt’s fight for independence, the king of Lan Xang offered Lê Lợi military assistance. When the Lao forces arrived in Đại Việt, however, they immediately took the side of the Chinese. Although the participation of Lan Xang’s forces in the war eventually proved to be short-lived, their action was seen by the Vietnamese as betrayal.