Complex sentence: This could be due to the fact that both private and public levels of debt are at historic highs in the U.S. and in many other countries, and a number of economists believe that excessive debt plays a role in causing bank crises and sovereign default.
Split into simpler sentences: This could be because both private and public levels of debt are at historic highs in the U.S. and in many other countries. A number of economists believe that excessive debt plays a role in causing bank crises and sovereign default.