The Reapers' War (, 1640–52) started as an uprising of peasants in Barcelona. Conflicts had already arisen between Catalonia and the monarchy in the time of Philip II. Having exhausted the economic resources of Castile, Philip wished to avail himself of those of Catalonia; the Catalan governmental institutions and laws were well protected by the terms of union of the kingdoms, and were jealously guarded by the Catalan population, who during those times increased its participation in the local and general government of the Principality. After Philip IV acceded to the throne in 1621, the Count-Duke of Olivares attempted to sustain an ambitious foreign policy by taxing the kingdoms of the Iberian Peninsula and establishing a military contribution to the Empire in each one of them (the "Unión de Armas", "Union of Arms"), which meant laying aside the until-then-prevailing principles of the composite monarchy, in favor of an increased centralization. Resistance in Catalonia was especially strong, given the lack of any significant apparent regional return for the sacrifices. The Catalan Courts of 1626 and 1632 were never concluded, due to the opposition of the estates against the economical and military measures of Olivares, many of which violated the Catalan constitutions. The failure of the Courts aggravated the tensions between Catalan institutions and Monarchy, favoring a scenario of rupture.