His research examines the interaction of religious sentiment, political thought and international relations in the sixteenth, seventeenth and eighteenth centuries.
It attempts to bridge the gap between the study of forms of cultural and intellectual expression and the realities of political, diplomatic and military organization.
He is one of the editors of a new series of monograph studies dedicated to the international impact of Spain, entitled the Historia de España y su proyección internacional, which is published by Albatros Ediciones in Madrid.
García Hernán's other principal area of interest lies in the relationship between Ireland, the Spanish Monarchy and the Papacy in the sixteenth-, seventeenth- and eighteenth-centuries.
García Hernán is an academic adviser to the editors of the new military history of Spain, Historia Militar de España, whose overall director is Hugo O´Donnell.