First Carlist War

The First Carlist War was a civil war in Spain from 1833 to 1840, the first of three Carlist Wars. It was fought between two factions over the succession to the throne and the nature of the Spanish monarchy: the conservative and devolutionist supporters of the late king's brother, Carlos de Borbón (or Carlos V), became known as Carlists (carlistas), while the progressive and centralist supporters of the regent, Maria Christina, acting for Isabella II of Spain, were called Liberals (liberales), cristinos or isabelinos. Aside from being a war of succession about the question who the rightful successor to king Ferdinand VII of Spain was, the Carlists’ goal was the return to a traditional monarchy, while the Liberals sought to defend the constitutional monarchy.

It is the largest and most deadly civil war in nineteenth-century Europe and fought by more men than the Spanish War of Independence. It might have been the largest counter-revolutionary movement in 19th-century Europe depending on the figures. Furthermore, it is considered the "last great European conflict of the pre-industrial age". The conflict was responsible for the deaths of 5% of the 1833 Spanish population—with military casualties alone amounting to half this number. It was mostly fought in the Southern Basque Country, Maestrazgo, and Catalonia and characterized by endless raids and reprisals against both armies and civilians.

Importantly, it is also considered a precursor to the idea of the two Spains that would surface during the Spanish Civil War a century later.