The article examines the relationship between public and private debt in advanced countries since 1870. It shows that financial stability risks mostly come from private sector credit booms, not public debt. However, high public debt levels can worsen the effects of private sector deleveraging after crises, leading to longer economic depressions. The study of 150 recessions since 1870 reveals that in a financial crisis, real GDP per capita drops by 5% and takes over 5 years to recover, compared to a 1.5% drop and 2 years recovery in a normal recession. Recovery is slower when a crisis follows a credit boom, and even worse when it coincides with high public debt levels.