Don Carlos contests his niece's succession, and he wins the fanatical support of the traditionalists of Aragon and of Basque Navarre (Spanish, Navarra).

The Carlists (supporters of Don Carlos) hold that legitimate succession is possible only through the male line.

Comprising agrarians, regionalists, and Catholics, the Carlists also oppose the middle class—centralist, anticlerical liberals who flock to support the regency.

The Carlists field an army that holds off government attempts to suppress them for six years (1833-39), during which time Maria Cristina receives British aid in arms and volunteers.

A Carlist offensive against Madrid in 1837 fails, but in the mountains, the Basques continue to resist until a compromise peace in 1839 recognizes their ancient fueros.

Sentiment for Don Carlos and for his successor remains strong in Navarre, and the Carlists continue  as a serious political force. Carlist uprisings will occur in 1847 and again from 1872 to 1876.