Isabella II (Spanish: Isabel; 10 October 1830 – 9 April 1904) was Queen of Spain from 1833 until 1868. She came to the throne as an infant, but her succession was disputed by the Carlists, who refused to recognize a female sovereign, leading to the Carlist Wars. After a troubled reign, she was deposed in the Glorious Revolution of 1868, and formally abdicated in 1870. Her son Alfonso XII became king in 1874.

Isabella was born in Madrid in 1830, the eldest daughter of King Ferdinand VII of Spain, and of his fourth wife and niece, Maria Christina of Bourbon-Two Sicilies. Queen Maria Christina became regent on 29 September 1833, when her three-year-old daughter Isabella was proclaimed sovereign on the death of the king.

Isabella succeeded to the throne because Ferdinand VII had induced the Cortes Generales to help him set aside the Salic law, introduced by the Bourbons in the early 18th century, and to re-establish the older succession law of Spain. The first pretender, Ferdinand's brother Carlos, fought seven years during the minority of Isabella to dispute her title. Carlos' and his descendants' supporters were known as Carlists, and the fight over the succession was the subject of a number of Carlist Wars in the 19th century.

Isabella's reign was maintained only through the support of the army. The Cortes and the Moderate Liberals and Progressives reestablished constitutional and parliamentary government, dissolved the religious orders and confiscated their property (including that of Jesuits), and tried to restore order to Spain's finances. After the Carlist war, the regent, Maria Christina, resigned to make way for Baldomero Espartero, Prince of Vergara, the most successful and most popular Isabelline general. Espartero, a Progressive, remained regent for only two years.

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