There are many perspectives on what development means and what causes underdevelopment. Todaro defines development as improving living standards, self-esteem, and freedom of choice in a multidimensional process. Alternative views see development as economic growth, modernization, or distributive justice. Marxist and dependency theories emphasize unequal international relationships. Popular development stresses local diversity and participation. Explanations of underdevelopment include vicious circles, colonial legacies, and the interaction of varied internal and external factors over time and place. No single theory can fully explain such a complex, varied phenomenon.