Up to the Peace of Prague, France had played a minimal part in the Thirty Years War. What participation France had committed herself to involved just diplomatic and political measures. Only in the relatively minor Mantuan episode did France have any military involvement but this was short-lived and did not involve the major European powers.
The Peace of Prague, arranged on Ferdinand’s terms, alarmed France, Sweden and the United Provinces. Sweden wanted to gain more territory to pay for her expenses up to the Peace and she decided to carry on fighting. However, Sweden was too poor to continue the campaign against Ferdinand by herself. In April 1635, Sweden and France signed the Treaty of Compiegne. France in the mid-1630’s was fearful of a strong and unchallenged Holy Roman Empire. She had an inadequate supply of men, money and commanders to sustain a long military campaign. France was also out-of-touch with the more modern methods of fighting that were coming to the surface in the Thirty Years War. Sweden could provide France with the necessary military expertise.
In the early months on 1635, France have vacillated over a wholesale military involvement in Europe. In February 1635, France had provided the Dutch with 20,000 men to deploy as the Dutch saw fit. In March 1635, France had once again cut off the Valtelline. The hand of France was forced for her when Spanish troops marched into Trier and captured the Archbishop Elector. Though a German state, Trier had been under French protection since 1631. In May 1635, France declared war on Spain. No-one throughout Europe was particularly surprised by this as in October 1634, the Holy Roman Emperor, King of Spain and the Roman Catholic princes of Germany had agreed to a joint attack on France. Louis XIII was simply pre-empting the inevitable : attack before France itself was attacked.
The military prospects of France were not good. Her troops were undisciplined and lacked experience in the more modern forms of fighting. France, therefore, needed alliances. In July 1635, France signed a treaty with Savoy, Parma and Mantua for a joint campaign in north Italy. The French Huguenot general, Rohan, was sent to help the Swiss Protestants in a campaign to overthrow the Valtelline. In October 1635, Bernard of Weimar and his army were taken into French service.
To sustain the above, Richelieu needed favourable finances. France was not in such a favourable position and Richelieu had to raise loans, sell government offices to the highest bidder (though not necessarily the most talented) and to place government tax inspectors (Intendants) on permanent location in the provinces to ensure that taxes that were due for Paris actually got there.
French military involvement in the Thirty Years War got off to a poor start. The Spanish made timely and generous concessions to the Swiss Protestants in the Valtelline and therefore stability was brought back to the area. Rohan was abandoned by the Swiss rebels and had to withdraw to France.
In 1636, came the expected attack on France by the major catholic powers of Europe. The high taxes in France had made Richelieu a very unpopular man and the invading Catholic forces hoped to capitalise on this and be seen as a liberating force with religion not being compromised. France had to endure a three-pronged attack.
The Cardinal-Infante attacked through Picardy. An Imperial army lead by Gallas attacked through the Vosges and Phillip IV of Spain lead an attack from the South.
The Cardinal-Infante was especially successful and many Parisians feared that their city would be occupied. It was commonly thought that Richelieu would be dismissed as a sop to the Cardinal-Infante but Louis XIII stood by him and asked Parisians to be patriotic and supply money to the government in the defence of Paris. Bernard of Weimar pushed back Gallas and the attack by Phillip IV failed to materialise. The Cardinal failed to maintain his push and he too was pushed back from Paris.
Though the attack on France failed, the prestige of France as a nation had suffered. She had proclaimed herself as the saviour against the domination of Europe by the Holy Roman Emperor, but how could a nation that had been invaded warrant the status of protector of European liberties ?
The German Electors had no faith in France . In the autumn of 1636 they were summoned to Regensburg by Ferdinand. Here, they duly elected his son, Ferdinand, King of the Romans. In February 1637, Ferdinand died and his son succeeded him as Ferdinand III. Like any new emperor or king, Ferdinand had to proved himself but his start was less than auspicious.
In October 1636, the Holy Roman Empire’s army had been defeated by the Swedes at Wittstock in Brandenburg. This gave Sweden the opportunity to occupy most of northern Germany. Gallas had to leave the French campaign and confront the Swedes. The Battle of Torgau forced the Swedes back to Pomerania and the Swedes could only stay in the field thanks to the financial aid given to them by the French in the Treaty of Hamburg of 1638. Regardless of the defeat at Torgau, Sweden marched into Bohemia and reached the suburbs of Prague.
France also had success in north Italy where Bernard of Weimar successfully besieged Breisach after defeating the Holy Roman Empire’s army at Rheinfelden. The siege of Breisach was a success and allowed the French to cut the Spanish Road once more. Alsace also fell to Bernard and when he died in July 19639, his army came under the direct control of the French. By 1640, France had two very capable military commanders : Turenne and Louis II, Prince of Conde.
The United Provinces also added to the misery of the Holy Roman Empire. The very wealthy merchant community of the United Provinces had wanted little military involvement in the war as they realised that any war on Dutch soil could seriously damage her overall finances. They believed that if the Dutch were seen by the Holy Roman Empire to be getting involved militarily in the conflict, it could lead to an invasion of the United Provinces by a Imperial army and that could spell disaster for the Dutch economy.
However, the Dutch had set their eyes on a naval success especially in the New World where Habsburg property was vulnerable to attack. Two naval battles supported their view that the Habsburg’s could not succeed at sea. In October 1639, the Dutch had beaten a Spanish fleet at the Battle of the Downs. In January 1640, a combined Spanish and Portuguese fleet had been beaten at the Battle of Pernambuco, again by the Dutch.
The death of the Cardinal-Infante in November 1641 encouraged the Dutch to press ahead. The Cardinal had put up a stubborn campaign on the land but the defeat of the Spanish navy at the Battle of the Downs, meant that he could no longer be supplied by sea and the Spanish campaign in Flanders dwindled.
The Spanish themselves were also experiencing problems at home. In 1640-41, the Portuguese rebelled against Spain. The Catalonians also rebelled against the domination of Castille in Spanish politics and a joint Catalan-French army defeated the Castillians outside of Barcelona in January 1641. Spain appeared to outsiders to be collapsing from within. In 1642, Phillip IV tried to crush the Catalan rebellion but failed. In January 1643, his most competent minister, Olivares, was dismissed.
France failed to capitalise on these problems as in December 1642, Richelieu had died, closely followed by Louis XIII in May 1643. The new king, Louis XVI, was only four years of age and a Regency had to be established. This Regency was lead by Anne of Austria, the Queen Mother, and the Italian, Mazarin. With this internal disruption, France could not follow a more aggressive foreign policy.
Despite defeating the Spanish at the Battle of Rocroi in May 1643, France was unable to mount a serious campaign in Europe as military exhaustion had broken out throughout Europe. There had been a general European desire for peace since 1640, but no one country was prepared to give up hard-won gains.
However, peace was not long in coming.