Answer the following question: Given the following passage  "Ferdinand refused and went to Valencia instead of Madrid. Here, on 17 April, General Elio invited the King to reclaim his absolute rights and put his troops at the King's disposition. The king abolished the Constitution of 1812. He followed this act by dissolving the two chambers of the Spanish Parliament on 10 May. Thus began six years (1814–1820) of absolutist rule, but the constitution was reinstated during the Trienio Liberal, a period of three years of liberal government in Spain from 1820–1823.",  answer the following question. Note that the answer is present within the text.  Question: What began on the 20th year of the 19th century?
Answer:
Trienio Liberal