From 1635, Piedmont had been forced to join France in its war against Spain, fighting principally against Spanish-controlled former Duchy of Milan, though its ruler, Victor Amadeus I, Duke of Savoy, avoided formally declaring war on Spain. In October 1637, Victor Amadeus died, and with his eldest son Francis Hyacinth only five years old, his will placed government under the regency of his widow Christine Marie of France, sister of Louis XIII of France. Despite her French origins, Christine did try to govern independently, she resisted French attempts to take over the regency, and on occasion she even stood up to personal bullying by Cardinal Richelieu; but Piedmont was so thoroughly dominated by its powerful neighbour that it could not follow an independent course, and Christine tended to be blamed for events over which she had no control. She did not help matters, however, by handing much of government over to her lover, Philippe d'Agliè. The late prince's brothers Thomas and Maurice had fears that they would be excluded from their rights to the succession, reinforced when, soon after the death of Victor Amadeus, Christine was forced by the French to write to the brothers insisting that they not return to Piedmont - though since Thomas was serving Spain at the time, the French demand was not entirely unreasonable. In 1638, Thomas sent his friend the marquis of Pallavicini to Turin, officially on a courtesy mission to Christine but actually to sound out public opinion in Piedmont on her rule; Maurice was also negotiating with other governments, including the Pope, to overturn Victor Amadeus' testament and end the regency of Christine, and soon was plotting simply to capture her. The situation became even worse in October 1638 when Francis Hyacinth died, and the succession passed to Charles Emmanuel, only four years old; although the testament of Victor Amadeus had made arrangements for a regency only for Francis Hyacinth, Christine continued as regent, but her legal position was much weaker, and her opponents argued that any regency for Charles Emmanuel had to be approved by the Estates, or by Piedmont's suzerain the Emperor, to be legitimate - there are suggestions that the Emperor had already declared Victor Amadeus' will void and Christine's regency invalid, but this is not reported by others. Late in 1638, Thomas went to Madrid to seek Spanish support for action he intended to take in Piedmont; since Spain was at war with Piedmont and France, he was bound to get some support, but there are suggestions that he tried, unsuccessfully, to ensure that Spain did not use the opportunity to make conquests from Piedmont for itself France was aware of Thomas' moves, and, expecting him to return to Piedmont privately, Richelieu issued orders 17 March 1639 to French commanders there to arrest him on sight and imprison him in Pinerolo, while Louis XIII wrote a threatening letter to his sister Christine forbidding her to allow Thomas to enter Piedmontese territory. However, Thomas and Maurice were preparing to come not as private individuals but with military force, allied to the Spanish: they concluded a treaty with Spain by which the brothers would keep any towns which opened their gates to them, while the Spanish would keep any towns that they took by force, a treaty sometimes described as effectively partitioning Piedmont between the brothers and Spain.
History
Invasion of Thomas and seizure of Turin, 1639
In early 1639 Thomas arrived in Milan, and late March, at the head of a small force, he entered Piedmont, where many towns promptly opened their gates to him, and Chivasso, just a short distance from Turin, submitted after a short siege. Negotiations with Christine and the French continued, however, and in April Richelieu even offered Thomas offices and a pension in France if he abandoned the Spanish cause. Thomas continued operating alongside the Spanish, and in late April, together with Leganés he initiated a formal siege of Turin; but the French troops in the city were too strong, so the siege was abandoned in favour of more field operations, while Thomas opened secret negotiations with supporters inside the city. Later in the year, in a surprise night attack co-ordinated with those supporters, Thomas managed to seize Turin - but only the city; Regent Christine fled into the citadel, still held by a large French force. After a failed attempt to recover the city from the citadel, Christine concluded a truce with Thomas until 24 October, during which both she and the French negotiated with him, sometimes at cross-purposes - at one point, Richelieu, annoyed at Christine's refusal to obey his every wish, hinted at the possibility of Thomas and Maurice replacing her as regent. When hostilities resumed after 24 October 1639, Thomas marched out of Turin and tried to catch the French field commander Harcourt as he was withdrawing from Chieri, but the Prince failed to co-ordinate his operations properly with the Spanish and was soundly defeated 19 or 20 November 1639 by Harcourt's rearguard under Turenne at the action variously known as Chieri or 'La Routa' or La Rotta ; Thomas showed great personal courage in the action, but his defeat was due mostly to his own incompetence. Another cease-fire was arranged over the winter, which Thomas spent holding Turin city, uneasily alongside the French in the citadel.
In the spring of 1640, Thomas entered the field again, and with the Spanish was again defeated by Harcourt at Casale. He returned to Turin, and was then involved in the subsequent siege of Turin, one of the most famous military events of the 17th century: French troops in the citadel were under attack by Thomas in the city, who was himself besieged by Harcourt and the French army - and when Leganés arrived with a Spanish relief force but dared not attack the French lines outright, Harcourt was himself besieged in his camp. Turin eventually had to consider surrender, and Thomas opened negotiations with Harcourt; unaware of orders en route from Paris that he was to accept nothing from Thomas except pure surrender as a prisoner or agreement to enter French service, Harcourt granted Thomas honourable terms in the capitulation signed on 20 September, and on 24 September Thomas marched out with his troops and withdrew to Ivrea.
Failed negotiations and the 1641 campaign
Over the winter, Thomas negotiated again with Richelieu, through the French agent, young Mazarin. Thomas was in a difficult position with his family still hostage in Madrid, but was prepared to see if he could secure terms that would get both Spain and France out of Piedmont and an end to the war being fought on Piedmontese territory. Richelieu seemed prepared to go some way to meeting his terms, and thought all was going well, but on 27 February 1641 Thomas unexpectedly renewed his treaty with the Spanish and resumed operations, which the French viewed as an act of great perfidy. Thomas tried besieging Chivasso but was forced by Harcourt to abandon the siege; he also failed in an attempted escalade of Cherasco.
Peace
In the autumn of 1641, Thomas' negotiations with Christine and the French resumed, and, although Richelieu was astonished at the scale of his demands given his defeats and the way he was being treated by the Spanish, French threats to deprive Thomas of any inheritance rights to the Soissons estate seemed to be having their effect and by 3 October the Cardinal thought that a settlement was in the bag. Final agreement took a little longer, but in 1642 Thomas settled with both France and Regent Christine: he was fed up with his Spanish 'allies' who were clearly using him to facilitate their own expansion into Piedmontese territory, she was fed up with the domineering conduct of the French; so they settled with each other and Christine then mediated a settlement between Thomas and the French, with both formal treaties being signed at Turin on 14 June 1642. Thomas' agreement with Christine included personal control of two major fortresses, Biella and Ivrea, for the duration of the regency, intended to provide him with security against possible reprisals. The Prince met with Christine on the road outside Ivrea, entered her coach and went with her to Turin, where he was wildly welcomed because their rapprochement meant the end of the civil war and at least a reduction in the devastation of the country - though not its end, because Piedmont had to continue fighting alongside France against Spain in the Franco-Spanish War of 1635-59.
