Homicides occur the world over, but they are not homogeneously distributed by geographical areas (continents, countries, regions), either over long or short periods of time, or in social groups, namely age, gender, social class or ethnicity. Why are there more homicides in some countries than in others? Why do killings increase in some countries, while they decrease in others? There are two fundamental schools of thought for social explanations of crime and violence: those attributing its origins to poverty and inequality and those blaming institutionalization or social norms. To discuss these theories, this paper analyzes and compares the changes in Colombia, Venezuela and Brazil in the first decade of the twenty-first century, where the homicide rate has decreased, increased and remained the same, respectively. Using the measurement of six variables (poverty, inequality, unemployment, national wealth, human development and the rule of law) and the technique of trajectory analysis, the results revealed that institutionalization is more to blame for the change than poverty and inequality. The text concludes that poverty and inequality affect crime and homicides, although not directly, but mediated by the institutions instead.