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, 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.

Don Carlos María Isidro Benito de Borbón y Borbón-Parma was an Infante of Spain and the second surviving son of King Charles IV of Spain and his wife, Maria Luisa of Parma. He claimed the throne of Spain after the death of his older brother King Ferdinand VII in 1833. His claim was contested by liberal forces loyal to the dead king's infant daughter, resulting in the First Carlist War (1833–1840). Don Carlos had support from the Basque provinces and much of Catalonia, but lost the war. His heirs continued the traditionalist cause, fought two more Carlist wars and were active into the mid-20th century, but never gained the throne.