Medical and public health innovations in the 1940s quickly resulted in significant health improvements around the world. Countries with initially higher mortality from infectious diseases experienced greater increases in life expectancy, population, and - over the following 40 years - social conflict. This result is robust across alternative measures of conflict and is not driven by differential trends between countries with varying baseline characteristics. At least during this time period, a faster increase in population made social conflict more likely, probably because it increased competition for scarce resources in low income countries.
Conflict = 0.617 * log(Population)
They say that this "implies that the average change (0.676) in log population from 1940 to 1980 leads approximately to 4.17 more years in conflict during the 1980s relative to the 1940s." In ordinary language, it means that a doubling of population leads to about 4.3 more years of conflict per decade. Here's their chart: