Viet Minh units occasionally made forays into Cambodian bases during their war against the French, and, in conjunction with the leftist government that ruled Thailand until 1947, the Viet Minh encouraged the formation of armed, left-wing Khmer Issarak bands. On April 17, 1950 (twenty-five years to the day before the Khmer Rouge captured Phnom Penh), the first nationwide congress of the Khmer Issarak groups convened, and the United Issarak Front was established. Its leader was Son Ngoc Minh (possibly a brother of the nationalist Son Ngoc Thanh), and a third of its leadership consisted of members of the ICP. According to the historian David P. Chandler, the leftist Issarak groups, aided by the Viet Minh, occupied a sixth of Cambodia's territory by 1952; and, on the eve of the Geneva Conference, they controlled as much as one half of the country.