According to some estimates, as many as 8 million slaves were taken from Angola, a figure higher than the total population of the country upon independence in 1975.  The slave trade caused major disturbances in the interior, with the associated violence and depopulation ultimately leading to the demise of the Kongo and other indigenous states.  The abolition of the international slave trade in the 1830s and of slavery throughout the Portuguese empire in the 1870s did not mark the end of forced African labor in Angola.  Domestic slavery, particularly among the Kongo chiefs and highland kings of the interior was still widespread and slaves continued to be exported to Indian Ocean markets further east.  Forced labor continued in a legal form under the new system of forced labor outlined in the 1878 Regulamento para os contratos de servicais e colonos nas provincias de Africa (Regulation for contracts of servants and colonists in the provinces of Africa).