The document examines the causes of changes in mortality in developing countries between 1950-2010. It finds that mortality declined due to technological advances like vaccines, antibiotics, and insecticides. Public health measures like improved sanitation, access to healthcare, and nutrition also contributed. The introduction of interventions like DDT spraying and improved access to medical services reduced deaths from diseases such as malaria, polio, and measles. Overall, declines in mortality were driven by improvements in public health, medicine, nutrition, and socioeconomic conditions in developing nations in the latter half of the 20th century.