As a result of that, the Arabized Christians progressively adopted the Romance language (medieval Spanish) at the expense of their Arab language, redefined their identity, and became assimilated into the new settler society during the 14th century. However, amidst its own assimilation, the Mozarab community was able to acculturate the northern Christians by providing them with part of their Arab and Muslim economic, legal, and notarial legacies. Historiographical Analysis Side by side with his research on Medieval Spanish history and particularly the Mozarab minority, Olstein paid attention to the history of historical writing on these topics contextualizing them in the changing socio-economic, intellectual, ideological, and political conditions throughout the nineteenth and twentieth centuries in Spain. Subsequently, his historiographical interests gravitated towards the varieties of macro-historical approaches - such as the world-system, historical sociology, and world history - that study the past on larger scales of space and time. In Thinking History Globally, Olstein outlines the research methods, agendas, and professional networks of twelve distinctive historical branches that frame their analysis of the past beyond closed boundaries: comparative, relational, international, transnational, oceanic, global, world, and big histories, history of globalization, historical sociology, world-system approach, and civilizational analysis. Beyond their singularities, the book arranges these twelve branches under the four big C’s for thinking history globally: comparisons, connections, conceptualizations, and contextualizations. Global and World History The conceptualization of the macro-historical approaches was followed by publications on world history. In “‘Proto-globalization’ and ‘Proto-glocalizations’ in the Middle Millennium” (Cambridge World History. Volume 5: Expanding Webs of Exchange and Conquest, 500-1500 CE), Olstein mapped the connections throughout the Eastern and Western hemispheres concluding that the Middle Millennium (a more ecumenical concept than the European Middle Ages for referring to the period 500-1500 CE) was made of a multiplicity of tiny local worlds, in which, nevertheless, regional and even hemispheric forces such as conquest, trade, and religious conversion had had defining impacts on local societies. In other publications on world history, Olstein moved beyond his expertise in medieval studies outlining broader arguments, for example, by periodizing world history according with three major regional divergences: the “Greatest divergence” starting by the end of the last Ice Age (ca. 15,000 before the present) and isolating the Old and the New Worlds from one another till ca. 1500; the “Great divergence” bifurcating the paths of Europe and Afro-Asia since ca. 1500; and the “American divergence” that divided the fortunes