of these Native slaves were exported to the Northern colonies and to off-shore colonies, especially the "sugar islands" of the Caribbean. The exact number of Native Americans who were enslaved is unknown because vital statistics and census reports were at best infrequent. Historian Alan Gallay estimates that from 1670 to 1715, British slave traders sold between 24,000 and 51,000 Native Americans from what is now the southern part of the U.S. Andrés Reséndez estimates that between 147,000 and 340,000 Native Americans were enslaved in North America, excluding Mexico. Even after the Indian Slave Trade ended in 1750 the enslavement of Native Americans continued in the west, and also in the Southern states mostly through kidnappings. Slavery of Native Americans was organized in colonial and Mexican California through Franciscan missions, theoretically entitled to ten years of Native labor, but in practice maintaining them in perpetual servitude, until their charge was revoked in the mid-1830s. Following the 1847–48 invasion by U.S. troops, the "loitering or orphaned Indians" were de facto enslaved in the new state from statehood in 1850 to 1867. Slavery required the posting of a bond by the slave holder and enslavement occurred through raids and a four-month servitude imposed as a punishment for Indian "vagrancy". Native Americans holding African-American slaves After 1800, some of the Cherokee and the other four civilized tribes of the Southeast started buying and using black slaves as labor. They continued this practice after removal to Indian Territory in the 1830s, when as many as 15,000 enslaved blacks were taken with them. The nature of slavery in Cherokee society often mirrored that of white slave-owning society. The law barred intermarriage of Cherokees and enslaved African Americans, but Cherokee men had unions with enslaved women, resulting in mixed-race children. Cherokee who aided slaves were punished with one hundred lashes on the back. In Cherokee society, persons of African descent were barred from holding office even if they were also racially and culturally Cherokee. They were also barred from bearing arms and owning property. The Cherokee prohibited the teaching of African Americans to read and write. By contrast, the Seminole welcomed into their nation African Americans who had escaped slavery (Black Seminoles). Historically, the Black Seminoles lived mostly in distinct bands near the Native American Seminole. Some were held as slaves of particular Seminole leaders. Seminole practice in Florida had acknowledged slavery, though not the chattel slavery