The causes of economic underdevelopment, and unequal distribution of wealth

International Relations scholars appear to disagree on the causes of economic underdevelopment, and unequal distribution of wealth among states. Neo-Marxist scholars explain these inequalities through a systemic theory, focusing on a world system that benefits some states disproportionally. Others argue that the causes of economic underdevelopment are to be found in unit-level attributes. Which of these two examples do you find most compelling? Why?