Medical innovations during the 1940s quickly resulted in significant health improvements around the world. Countries with initially higher mortality from infectious diseases experienced larger increases in life expectancy, population and subsequent social conflict. This cross-country result is robust across alternative measures of conflict, and is not driven by differential trends between countries with varying baseline characteristics. A similar effect is also present within Mexico. Initial suitability conditions for malaria varied across municipalities, and anti-malaria campaigns had differential effects on population growth and social conflict. Both across countries and within Mexico, increased conflict over scarce resources predominates and this effect is more pronounced during times of economic hardship (specifically, in countries with a poor growth record and in drought-stricken areas in Mexico). At least during this time period, a larger increase in population made social conflict more likely.