 Emperor Ferdinand II used his rights as feudal overlord to prevent the heir, the French Duke of Nevers, from taking over the Duchy, leading to the War of the Mantuan Succession, a part of the much larger Thirty Years' War.In the early 18th century, during the War of the Spanish Succession, imperial claims to suzerainty were used again to seize Mantua in 1708, which was now attached by the Austrian Habsburgs to the newly conquered Duchy of Milan.The Duchy of Milan itself was occupied by Austria on the basis that it was a vacant Imperial fief.