 Maddison was a pioneer in the field of the construction of national accounts, where a country's accounts are calculated back in periods of several decades all the way to the year 1.To this end he combined modern research techniques with his own extensive knowledge of economic history and in particular countries' performances in the field of GDP per capita.His work resulted in a deep new understanding of the reasons why some countries have become rich whereas others have remained poor (or have succumbed to poverty).