In September of 1868 the French Empire intervened in Spain following the overthrow of Queen Isabella II. Many historians see this as a sign of Emperor Napoleon III's increasingly ambitious foreign policy, if not outright expansionism.
At the time of the uprising, Isabella was in France to negotiate a treaty of alliance with the Emperor. She soon hurried back to Madrid, but was too late to prevent the defeat of royalist forces at the Battle of Alcolea on the 28th. As a result, Isabella fled to Paris with much of her court, and beseeched Napoleon III for support.
Napoleon could see that it would be political madness to attempt a restoration of Isabella. However, Spain's search for a new king could be used to increase French influence in her southern neighbour. On the 3rd of October, a French delegation arrived at the Cortés, informing the body of Napoleon's displeasure at the coup d'etat.
Nevertheless, a compromise was proposed - that Isabella's son Alfonso be made king instead. Many in the Cortés had already considered him for the throne. At the end of October, Alfonso returned to Madrid sans Isabella, and was declared King by the Cortés - the beginning of a true constitutional monarchy.
As part of the negotiations, several French advisors were dispatched to help initiate vital reforms.
Months of Anarchy
However, large sections of the military were dissatisfied with the election of Alfonso. In the months that followed mutinies were rife, and the government lost control of parts of the country. There was little loyalty to the new king, and every week more generals defected to the rebel side.
Just as in Belgium, the government was pushed to seeking French help to restore order. The Council of Regency, persuaded by its French advisors, sent a request for intervention to Napoleon III towards the end of the year.
The military made preparations for a large scale expedition. By now, larger towns such as Barcelona had fallen to the liberal forces. The Spanish Expedition of 1823 number less than 90,000. For this operation and army of some 200,000 men was assembled at the border over a period of two months.
By the end of February, as France prepared to enter the conflict, Spain was in anarchy, with the rebels slowly encircling Madrid.
On the 3rd of March 1869, the Armée de l'Espagne was finally ready to enter the country. Within weeks, detachments besieged revolting cities in Catalonia and other parts of Spain. Joined by Spanish loyalist forces, the French pushed the rebels back from the outskirts of Madrid. Several minor defeats led the revolutionary army to pull back to Cadiz.
Aware that retreating behind the city walls would lead to certain defeat after a lengthy siege, Marshall Prim made ready to attack the Franco-Spanish army in the field. The Battle of Cadiz was, nevertheless, a quick affair, and the revolutionary army disbanded. By the end of April all rebellious cities had surrendered and peace had been restored.
Napoleon III was able to impose a permanent French occupation upon the Cortés, supposedly to ensure stability and safeguard young Alfonso's rule. 90,000 French soldiers remained stationed in Spain. Their presence turned Spain into a French client state, with the advice of French supervisors accepted by the Regency Council and the Cortés left toothless.
However, the French military presence enabled the government to impose economic and social reforms across all the provinces, against the objections of regional parties and the formerly-influential generals. As a result, Spain slowly began to recover from decades of instability.