the differences between how native american and black identities are defined today (blood quantum versus one-drop and political assumptions) have been based on different historical circumstances. according to the anthropologist gerald sider, such racial designations were a means to concentrate power, wealth, privilege and land in the hands of whites in a society of white hegemony and privilege (sider 1996; see also fields 1990). the differences had little to do with biology and more to do with the history of slavery and its racism, and specific forms of white supremacy (the social, geopolitical and economic agendas of dominant whites "vis-à-vis" subordinate blacks and native americans). they related especially to the different social places which blacks and amerindians occupied in white-dominated 19th-century america. sider suggests that the blood quantum definition of native american identity enabled mixed-race whites to acquire amerindian lands during the allotment process. the one-drop rule of black identity, enforced legally in the early 20th century, enabled whites to preserve their agricultural labor force in the south. the contrast emerged because, as peoples transported far from their land and kinship ties on another continent, they became reduced to valuable commodities as agricultural laborers. in contrast, amerindian labor was more difficult to control; moreover, amerindians occupied large territories that became valuable as agricultural lands, especially with the invention of new technologies such as railroads. sider thinks the blood quantum definition enhanced white acquisition of amerindian lands in a doctrine of manifest destiny, which subjected native americans to marginalization and resulted in numerous conflicts related to american expansionism.