 This emphasis changed after independence, in response to the pressing needs for national development and progress. Positivist philosophers, such as Sarmiento, frequently advocated national policies that favored European immigration as a way of undermining the racial and ethnic differences that divided the population (see Burke and Humphrey in Gracia, 2011). These policies were often based on a negative view of both Amerindians and Africans. Moreover, these policies failed to achieve the goals their proponents sought. The failure of positivist ideas to help define the identity of the populations of the various nations gave rise to a reaction, most evident in the Mexican Revolution, to turn back to the Amerindian past as a way to find a unity that would make nations of the diverse population. Notions of both national and Latin American unity were proposed on various grounds at this time. For some, as is the case with Vasconcelos, the unity is racial, a result of the mixing of the various races that constitute the Latin American populations (see von Vacano in Gracia, 2011). For others—such as Zea—the cultural unity of these populations provided the basis of national or Latin American identity (see Oliver in Gracia, 2011).