Some particular features of two periods in the history of Great Spanish Monarchy in the age of its global dominance are considered in the article. They are the period of its unprecedented prosperity and the following one of its unexpected economiс and political decay, transforming the Spanish empire into a secondary-rate European state. The author examines causes of that negative process contrary to the events taken place in other European countries where national bourgeois states and capitalist productive relations were being formed. On the basis of researches of the foreign and Russian historians and the factual data collected in their studies the author presents his vision on the problem analysing economic and social factors of the age of primitive capital accumulation which proved to be decisive in the defeat of Spanish monarchy in struggle with its main historical rivals England and France. A special attention is given to the analysis of the empire governance structure both in its overseas territories and hinterland. Focusing on the economic policy of the Castialian monachs the author underlines its highly negative role in the development of trade, industry and agriculture, new progressive forms of economic life.”Castilianization” of the state budget, financial and credit policy was directed on securing the interest of the narrow social and regional stratum of rich castillian aristocracy at the expense of colonial robbery and extreme exploitation of castillian productive population. It finally resulted in exhaustion of domestic and external resources of capital accumulation, depopulation, financial bankruptcy and further political degradation of Spanish empire.