Queen Isabel II was overthrown by a conspiracy of liberal Generals, and left Spain in some disgrace. The generals replaced her with a Amadeo, the Duke of Aosta (and second son of King Victor Emmanuel of Italy), Then when the Spanish elections of 1872 resulted in a swing away from the Carlists, the Carlist pretender, Carlos VII, decided that only force of arms can win him the throne.
I’m in the process of building the armies the Oriamendi Campaign. This involves both the British Auxiliary Legion and the French Foreign Legion, plus a good cross section of Spanish troops. My armies are based on the Orders of Battle for the Oriamendi Campaign. Initially they cover all the troops mentioned for the Battle of Oriamendi (Hernani), plus some significant extras from supporting forces … like the Cristino Guard Division and the French Foreign Legion.
In 1830 the French both invaded Algeria and disbanded the seven regiments of Swiss and Germans in the French Army (Windrow, 1981) . To feed the former action and get the disgruntled ex-soldiers off the streets they created the ‘Foreign Legion’ for service outside continental France (9 Mar 1831). The battalions were organised in the same way as the French Line Infantry with eight companies of 112 men . Initially there were no flank companies, but in Apr 1832 the battalions were each permitted to convert two of their fusilier companies into elite units, one of Grenadiers and one of Light Infantry (Voltigeurs). The Legion entered combat on 27 Apr 1832. They received their first flag in Jun 1832.
At the start of the First Carlist war the liberal army has structured as per the Royal Decree of 31 May 1828 (Alcalá, 2006).
In May 1835 the Spanish government asked the British for permission to raise a force of 10,000 volunteers for service against Don Carlos in the First Carlist War (Spiers, 1983). The British agreed, seeing this as a better alternative to direct intervention, although they did also provide regulars in support. The British Auxiliary Legion was sanctioned in Jun 1835 with the first detachments arriving in Spain on 10 Jul. The initial full strength of 7,800 was on the ground by the end of Oct. Of the first contingent 3,200 were English, 2,800 were Irish and 1,800 Scots. Most were civilians with no military experience, including the officers. The men enlisted in the Spanish army, but under British conditions of service.