 During the Joseon period, in times of poor harvest and famine, many peasants voluntarily sold themselves into the nobi system in order to survive.In Southeast Asia, there was a large slave class in Khmer Empire who built the enduring monuments in Angkor Wat and did most of the heavy work.Between the 17th and the early 20th centuries one-quarter to one-third of the population of some areas of Thailand and Burma were slaves.