The history of Spain dates back to the Early Middle Ages. In 1516, Habsburg Spain unified a number of disparate predecessor kingdoms; its modern form of a constitutional monarchy was introduced in 1813, and the current democratic constitution dates to 1978. A tenuous balance between liberal and conservative forces was struck in the establishment of constitutional monarchy during 1874–1931 but brought no lasting solution, and Spain descended into Civil War between the Republican and the Nationalist factions.