War of the Mantuan Succession

The War of the Mantuan Succession (1628–31) was a peripheral part of the Thirty Years' War. Its casus belli was the extinction of the direct male line of the House of Gonzaga in December 1627. Brothers Francesco IV (1612), Ferdinando (1612–26) and Vincenzo II (1626–27), the last three dukes of Gonzaga, had all died leaving no legitimate heirs. The war, fought among the backers of rival claimants, pitted France against the Habsburgs in a contest for control of northern Italy.

Background
Mantua is the ancestral city where the male line of the Gonzaga dynasty ruled, first as marquesses, then after 1540 as dukes, in vassalage to the Holy Roman Empire.

Monferrato was a duchy since 1574 on the eastern side of Piedmont, and an imperial fief since the eleventh or twelfth century. The Gonzagas had enlarged their realm with Monferrato after receiving it in dowry from the wife of duke Frederick II Gonzaga.

On 22 September 1612, Francis IV, Duke of Mantua and Monferrato died at the age of 26. His death occurred only a couple of months after the death of his father Vincent I, Duke of Mantua. He left only a three-year old daughter, Maria of Mantua. Francis IV also had two younger brothers who, both being cardinals of the Church and consecrated priests, could not marry and were thus ineligible to succeed to Mantua's throne.

Nonetheless, Francis' two brothers, Ferdinando I (1587–1626) and Vincenzo II (1594–1627), eventually did become Dukes of Mantua. Despite hastily marrying via "ecclesiastical revisions," neither produced any legitimate children. A crisis erupted when Vincenzo II died on 26 December 1627 at the age of 33, the same day that his niece Maria Gonzaga's marriage with Charles de Nevers was celebrated. Nevers was the eldest son and heir of Charles, Duke of Nevers, Rethel and Mayenne. Moreover, he was the head of the cadet branch of the House of Gonzaga, and after Vincenzo II, heir male of the Duchy of Mantua.

The claimants, and their supporters
The Duke of Nevers was a son of Luigi, younger brother of Vincenzo II's grandfather (see family tree). Luigi had been naturalized French as Louis about 1550, and married the heiress of the duchies of Nevers and Rethel in 1566. For the French Crown Nevers, a French peer, would naturally be preferable as ruler in Mantua. Nevers arrived there in January 1628 and proclaimed its sovereign.

There were two rival claimants. One was Charles Emmanuel I, Duke of Savoy, whose daughter Margaret was the widow of Francis IV. Although their son had died an infant in 1612, it was their elder daughter Maria (1612–1660) who had married Charles de Nevers in 1627. Charles Emmanuel based his right to Mantua on his daughter's claim to a substantial portion of the Gonzaga realm, the duchy of Montferrat, which was demonstrably heritable by females since the Gonzagas had acquired it through marriage to Margherita Paleologa in 1540.

The other claimant was Ferrante II, Duke of Guastalla, a distant Gonzaga cousin who voiced his claim but did not immediately place troops in the field. He was, however, supported by Emperor Ferdinand II, whose wife at the time, Eleanor of Mantua the elder (1598–1655), had been the sister of the last three Dukes of Mantua. He sought to re-attach the Duchy of Mantua to the Holy Roman Empire; Ferrante being in the Spanish-Imperial camp, was a useful tool to that purpose.

But as the Thirty Years War wore on, it affected dynastic alliances. Charles Emmanuel obtained support from the Habsburgs, who controlled Milan. The resulting French-Habsburg war over the succession was just one of the many theatres of the Thirty Years War, fought all over Europe.

Conflict
The initial attempt of Don Gonzalo Fernandez de Córdoba, Spanish governor of Milan, and Charles-Emmanuel was to partition the Mantuan-Montferrat patrimony, which lay to east and to west of Milan. The Spanish minister supported the Guastalla claimant in Mantua, as the weaker of two neighbors, and the Savoy claimant in Montferrat, the lesser of the territories. Friction between the confederates ensued, when Charles-Emmanuel moved his troops into more territory than had been agreed upon, laying siege to the town of Casale, capital of Montferrat.

The French, although Louis XIII of France and Cardinal Richelieu were concerned at home with Huguenot uprisings in Languedoc after the fall of La Rochelle in 1628, sent forces to relieve Casale near the border with Milanese territory, besieged by a Habsburg army from Milan. The French forces crossed the Alps in March 1629, forced Susa in Piedmont, on 6 March, delivered the siege of Casale on 18 March 1629 and took the fortress of Pinerolo on 30 March 1630. In the meantime the short-lived Treaty of Susa was signed with the Duke of Savoy in April 1629, whereupon they returned to France, leaving behind a small garrison. The papal envoy in negotiations at Casale was Jules Mazarin.

Emperor Ferdinand II's forces under Ramboldo, Count of Collalto invaded the Grisons and Valtelline. The governor was recalled from Milan, followed by the insults of the citizens, for bread had been scarce for months. The following winter, Milan was devastated by the bubonic plague introduced by the armies, which has been vividly described by Manzoni.

Later in 1629, Emperor Ferdinand II sent a Landsknecht army to besiege Mantua. Charles left without the promised support from Louis XIII of France. The siege lasted until July 1630, when the city, already struck by a plague, was brutally put to the sack for three days and three nights by troops led by Count Aldringen and Gallas. But the Emperor did not succeed in Mantua. Due to developments in Germany, where the Swedes were warring, he was forced to return his attention to the principal theatre of the big war.

The Peace of Regensburg (1630)
The French first agreed to the Peace of Regensburg (or the Treaty of Ratisbonne), which was negotiated by French representatives Father Joseph and Nicolas Brûlart de Sillery. The accord was signed on 13 October 1630, which provided favorable terms to French interests in Italy despite their military setbacks. Specifically, the French were allowed to maintain their garrison in Grisons. The accord also confirmed Charles Gonzaga-Nevers as Duke of Mantua and Marquess of Monterrat in exchange for minor concessions to Charles Emmanuel of Savoy and Ferrante of Guastalla. The Habsburgs would on their side reduce their number of troops in the region. The treaty was seen as so unfavorable to the Spanish that the Spanish prime minister, Olivares, considered it no different than a surrender.

The treaty, moreover, contained a troublesome clause. It included an agreement whereby the French were not permitted to establish alliances in Germany against a reigning Holy Roman Emperor. This should have sidelined France in the ongoing conflict. Louis XIII of France refused to accept this, and the Austrians found themselves still at war, yet with diminished forces in the area. The new forces sent south of the Alps were to be sorely missed when Swedish forces under Gustavus II Adolphus invaded from the north.

The Treaty of Cherasco (1631)
The Italian peace was eventually made with the Treaty of Cherasco, signed in a city in Piedmont on 19 June 1631. France, which in 1629 had taken Savoy, then captured Pinerolo in Piedmont the following year, renounced its conquests in Italy. Charles Gonzaga-Nevers was confirmed as ruler in Mantua and Montferrat, with concessions to the other claimants: Vittorio Amedeo I, who succeeded in Savoy after the sudden death of his father, Duke Charles Emmanuel, gained Trino and Alba in Montferrat; while Cesare II of Guastalla, Ferrante's son, was given Luzzara and Reggiolo. Later it was discovered that by a secret treaty with Vittorio Amedeo, Pinerolo was surrendered to France.