Soon after the beginning of the Cold War his marxist conceptions, though undogmatic, had placed him in relative isolation, and in 1949 he was denied entry to the United States for an intended speaking engagement at an international scholarly conference in Princeton of which he was one of the initiators. Instead, he was welcomed as a guest professor in the young republic of Indonesia during the 1951–1952 academic year. He devoted the latter part of his life to writing a history of Europe during the 25-year period from 1889 to 1914: "The Watershed of Two Eras. Europe in 1900", which was published posthumously in 1967 (English edition 1978). According to various reviewers it "is a highly successful attempt at writing an analysis and synthesis of European history between the years 1890 and the outbreak of the First World War", the decades during which Europe's supremacy in the world started waning. "This is one of the best books of its kind of integrated history. (...) Romein has successfully integrated the various branches of history - economic, cultural and political - without being stilted. (...) This work can be read with great profit by the highly educated general reader, the undergraduate history major, the advanced graduate student, and the professional historian." The book devotes chapters to all aspects of European history during this period: not only economic, social, cultural and political history, but also the developments in science, medicine, law and criminology, psychology, literature, art, women emancipation, religion and atheism, education etc. "The American Historical Review" concluded: "the book is a treasury of illuminating fact and perceptive commentary." Due to a chronic illness, which became manifest in 1959, he limited his professorship at the University of Amsterdam to solely Theoretical History. He died in Amsterdam in July 1962.