However, William Woodthorpe Tarn, between World War I and World War II and the heyday of the League of Nations, focused on the issues of racial and cultural confrontation and the nature of colonial rule. Michael Rostovtzeff, who fled the Russian Revolution, concentrated predominantly on the rise of the capitalist bourgeoisie in areas of Greek rule. Arnaldo Momigliano, an Italian Jew who wrote before and after the Second World War, studied the problem of mutual understanding between races in the conquered areas. Moses Hadas portrayed an optimistic picture of synthesis of culture from the perspective of the 1950s, while Frank William Walbank in the 1960s and 1970s had a materialistic approach to the Hellenistic period, focusing mainly on class relations. Recently, however, papyrologist C. Préaux has concentrated predominantly on the economic system, interactions between kings and cities and provides a generally pessimistic view on the period. Peter Green, on the other hand, writes from the point of view of late 20th century liberalism, his focus being on individualism, the breakdown of convention, experiments and a postmodern disillusionment with all institutions and political processes.