The Spanish Civil War of 1820–1823, fought in the aftermath of the Napoleonic Wars, is a conflict between royalists and liberals with France intervening on the side of the royalists.

The revolutionaries of 1820 succeed in forcing the monarchs of Spain and the southern Italian kingdom of the Two Sicilies to grant liberal constitutions against their wills.

The Trienio Liberal ("Liberal Triennium") is a period of three years in the modern history of Spain between 1820 and 1823, when a liberal government rules Spain after a military uprising in January 1820 by the lieutenant-colonel Rafael de Riego against the absolutist rule of King Ferdinand VII.

It ends in 1823 when, with the approval of the crowned heads of Europe, a French army invades Spain and reinstates the King's absolute power.

This invasion is known in France as the "Spanish Expedition" (expédition d’Espagne), and in Spain as "The Hundred Thousand Sons of St. Louis".