To temper their counter-revolutionary ardor, the Duc de Richelieu deployed troops along the Pyrenees Mountains along the France-Spain border, charging them with halting the spread of Spanish liberalism and the "yellow fever" from encroaching into France.

On 22 January 1823, a secret treaty, from which Britain was excluded, was signed at the Congress of Verona, allowing France to intervene in Spain to help restore Ferdinand VII as an absolute monarch.

Chateaubriand and the ultra-royalists rejoiced; the royal army was going to prove its bravery and devotion in the face of Spanish liberals, fighting for the glory of the Bourbon monarchy.

The superintendent of the military was unable to assure logistic support for the expedition's 95,000 men (as counted at the end of March) concentrated in the Basses-Pyrénées and the Landes with 20,000 horses and 96 artillery pieces.

To remedy his doubts, he had to consult the munitions-supplier Ouvrard, who quickly concluded that marches in Spain were as favourable to his own interests as to those of the army, even if they would be to the detriment of the public treasury.

The expedition was made up of regiments in which many of the officers, NCOs and men had been marked by memories of the Napoleonic Wars and so were disposed more kindly towards the liberals than were the French and Spanish Bourbons.

Many of them joined Englishmen under Colonel Robert Wilson, Belgians under Jan Willem Janssens and other French or Italian volunteers to form a liberal legion and a squadron of "liberty lancers" to fight beside the Spanish constitutional forces.

The following day, on 7 April, the "100,000 Sons of Saint Louis" under the Duke of Angoulême entered Spain without opposition from the constitutional government's forces and with the support of the middle classes and part of the urban population.

The French were left in control of the rural parts of Navarre, Asturias and Galicia; however, lacking siege equipment, they were unable to blockade the towns, where the liberals continued to resist for several more months.

More decisive operations spread across Andalusia, since it was the site of Cádiz, transformed into the Constitutionalists' provisional capital and thus the French force's main strategic objective.

Forced to use several naval divisions for surveillance of Spain's Atlantic and Mediterranean ports and coasts (held by the Constitutionalists), the French navy was able to spare only a small squadron of 10 ships under Counter-Admiral Jacques Félix Emmanuel Hamelin to blockade the city.

That proved too small a force for Hamelin to succeed in this mission and so on 27 August he was replaced by Counter-Admiral des Rotours, then by Duperré, who arrived only on 17 September, with meagre reinforcements.

However, on 1 October 1823, feeling bolstered by French forces, Ferdinand broke his oath and again repealed the Constitution of Cádiz and declared null and void all the acts and measures of the liberal government.