What accounts for the fall in long-term interest rates in the United States and the core euro-zone countries?

Since the summer of 2018, long-term interest rates have been falling in the United States and the core euro-zone countries. Yet, non-residents ar e sellers of US bonds, euro-zone bonds and those issued by the core euro-zone countries, which could have driven up long-term interest rates. The fall in the interest rates in the United States and the core euro-zone countries must then be due only to resident, domestic investors in these countries switching from risky assets (equities, corporate and bank bonds, and bonds issued by troubled countries) to risk-free bonds. It is interesting to see that government bonds remain risk-free only for the country’s domestic investors.