A number of theories have appeared in the study of international relations that are particularly relevant to Latin America, and some have been formulated with particular reference to the region. The principal theories include the realist-idealist dichotomy, the Marxist critiques and alternatives, liberal developmentalism with its various shades of analysis, and the variants of dependency theory. Practices associated with realism—balance-of-power, strategic, and geo-political calculations, and conflict—have been important aspects of the Latin American subsystem from its beginnings to the present. European imperialism in Latin America during the nineteenth century took on special characteristics. Latin American leaders also formulate policies in terms of national interests based on theories of national security. Comparative political analysis has purported to place Latin America in a larger than regional mold in terms of development theory and the concept of modernization. Development theory has provided the basis for a significant portion of US policy in Latin America.