The Trienio Liberal was a three-year period of liberal government in Spain that lasted from Rafael del Riego's 1820 uprising until the "Hundred Thousand Sons of Saint Louis" invasion of 1823. De Riego and liberal army officers forced King Fernando VII of Spain to agree to rule in accordance with the liberal constitution of 1812, which he had previously ignored, briefly establishing a constitutional monarchy. In 1823, following the Congress of Vienna, the Kingdom of France invaded Spain with 95,000 troops, defeating the liberals and restoring the absolute monarchy.