When Ferdinand VII of Spain died in 1833, his fourth wife Maria Cristina became Queen regent on behalf of their infant daughter Isabella II. This splintered the country into two factions known as the Cristinos (or Isabelinos) and the Carlists. The Cristinos were the supporters of the Queen Regent and her government. The Carlists were the supporters of Carlos, a pretender to the throne and brother of the deceased Ferdinand VII. The First Carlist War lasted over 7 years and the fighting spanned most of the country at one time or another, although the main conflict centered around the Carlist homelands of the Basque Country and Aragon.
Queen Isabella 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.