Pestilences, like that of 1628/1630, and the generally declining conditions of Italy's economy in the 17th and 18th centuries halted the further development of Northern Italy. The only polity that managed to thrive in this period was the Savoy's state which, thanks to military and diplomatic victories in 1720, managed to acquire the island of Sardinia, through which the then Dukes gained legitimacy as a proper Kingdom and increased Turin's importance as a European capital.