In 1349 Fa Ngum was granted an army known as the "Ten Thousand" to take the crown. At the time the Khmer Empire was in decline (possibly from an outbreak of the Black Death and the combined influx of Tai peoples), both Lanna and Sukhothai had been established in what had been Khmer territory, and the Siamese were growing in the area of the Chao Phraya River which would become the Ayutthaya Kingdom. The opportunity for the Khmer was to create a friendly buffer state in an area they could no longer effectively control with only a moderately sized military force.