What has triggered the trend rise in public debt ratios?

We see an upward trend in public debt ratios from the early 1980s in the United States and the euro zone. What are the factors triggering this upward trend in public debt ratios? Not the level of interest rates, since they are becoming increasingly low relative to the growth rate; At first sight, they may include: Additional public spending needs, in particular due to population ageing; The lowering of the tax burden due to tax competition; The succession of severe crises that have require d the use of a highly expansionary fiscal policy, which governments do not dare to reverse completely after the crises; A compensation for the decline in private debt. The relevant explanations seem to be: The increase in the weight of pension and healthcare spending; Tax competition; The succession of crises; Only from 2009 to 2019, private sector deleveraging.