whose success forced the Spanish-Savoyard alliance to withdraw from Casale and sign the Treaty of Cherasco in April 1631. Nevers was confirmed as Duke of Mantua and although Richelieu's representative, Cardinal Mazarin, agreed to evacuate Pinerolo, it was later secretly returned under an agreement with Victor Amadeus I, Duke of Savoy. With the exception of the 1639 to 1642 Piedmontese Civil War, this secured the French position in Northern Italy for the next twenty years. After the outbreak of the Franco-Spanish War in 1635, Richelieu supported a renewed offensive by Victor Amadeus against Milan to tie down Spanish resources. These included an unsuccessful attack on Valenza in 1635, plus minor victories at Tornavento and Mombaldone. However, the anti-Habsburg alliance in Northern Italy fell apart when first Charles of Mantua died in September 1637, then Victor Amadeus in October, whose death led to a struggle for control of the Savoyard state between his widow Christine of France and brothers, Thomas and Maurice. In 1639, their quarrel erupted into open warfare, with France backing Christine and Spain the two brothers, and resulted in the Siege of Turin. One of the most famous military events of the 17th century, at one stage it featured no less than three different armies besieging each other. However, the revolts in Portugal and Catalonia forced the Spanish to cease operations in Italy and the war was settled on terms favourable to Christine and France. In 1647, a French-backed rebellion succeeded in temporarily overthrowing Spanish rule in Naples. The Spanish quickly crushed the insurrection and restored their rule over all of southern Italy, defeating multiple French expeditionary forces sent to back the rebels. However, it exposed the weakness of Spanish rule in Italy and the alienation of the local elites from Madrid; in 1650, the governor of Milan wrote that as well as widespread dissatisfaction in the south, the only one of the Italian states that could be relied on was the Duchy of Parma. Catalonia Throughout the 1630s, tax increases levied to pay for the war led to protests throughout Spanish territories, which in 1640 resulted in simultaneous revolts first in Portugal, then the Principality of Catalonia. Backed by France as part of Richelieu's 'war by diversion', in January 1641 the rebels proclaimed a Catalan Republic. The Madrid government quickly assembled an army of 26,000 men to crush the revolt, which defeated the rebels at Martorell on