Real interest rates have been low for a long time, and the usual explanation that they are driven by saving and investment doesn't seem to hold up when looking at data from 19 countries since 1870. Instead, changes in real interest rates seem to be more closely linked to shifts in monetary policies. Global interest rates are influenced more by individual countries' actions rather than overall saving and investment trends. This suggests that monetary policy plays a bigger role in determining real interest rates over the long term.