Laws were promulgated in Spain in 1542 to protect isolated natives, but the abuses in the Americas were never entirely or permanently abolished. The Spanish also employed the pre-Columbian draft system called the mita, and treated their subjects as something between slaves and serfs. Serfs stayed to work the land; slaves were exported to the mines, where large numbers of them died. In other areas the Spaniards replaced the ruling Aztecs and Incas and divided the conquered lands among themselves ruling as the new feudal lords with often, but unsuccessful lobbying to the viceroys of the Spanish crown to pay Tlaxcalan war demnities. The infamous Bandeirantes from São Paulo, adventurers mostly of mixed Portuguese and native ancestry, penetrated steadily westward in their search for Indian slaves. Serfdom existed as such in parts of Latin America well into the 19th century, past independence. Historian Andrés Reséndez argues that even though the Spanish were aware of the spread of smallpox, they made no mention of it until 1519, a quarter century after Columbus arrived in Hispaniola. Instead he contends that enslavement in gold and silver mines was the primary reason why the Native American population of Hispaniola dropped so significantly. and that even though disease was a factor, the native population would have rebounded the same way Europeans did following the Black Death if it were not for the constant enslavement they were subject to. He further contends that enslavement of Native Americans was in fact the primary cause of their depopulation in Spanish territories; that the majority of Indians enslaved were women and children compared to the enslavement of Africans which mostly targeted adult males and in turn they were sold at a 50% to 60% higher price, and that 2,462,000 to 4,985,000 Amerindians were enslaved between Columbus's arrival and 1900. Massacres The Pequot War in early New England. In mid-19th century Argentina, post-independence leaders Juan Manuel de Rosas and Julio Argentino Roca engaged in what they presented as a "Conquest of the Desert" against the natives of the Argentinian interior, leaving over 1,300 Indigenous dead. While some California tribes were settled on reservations, others were hunted down and massacred by 19th century American settlers. It is estimated that at least 9,400 to 16,000 California Indians were killed by non-Indians, mostly occurring in more than 370 massacres (defined as the "intentional killing of five or more disarmed combatants or largely unarmed