After Christopher Columbus arrived to America for the first time in 1492, a discovery and conquest frenzy began. In 1520, Ferdinand Magellan crossed the strait that now bears his name. Years later, Pedro de Valdivia, the main conquistador of Chile, put together an expedition to the southern seas and the strait of Magellan. The objective was to compile geographical information to aid ships coming from Spain when they sailed through the area. Captain Francisco de Ulloa was in charge of the expedition, which arrived to the Chacao canal in 1553. The Spaniards covered the entire coast of Chiloe, establishing landmarks and naming ports, islands and canals.
Ulloa is considered the first explorer and discoverer of Chiloe. In February of 1558, Juan Fernandez Ladrillero travelled south in search of new land to conquer for the Spanish crown under orders from Garcia Hurtado de Mendoza, governor of Chile. He was the first person to come into contact with the aborigines that lived in the Chiloe archipelago.
In September of that same year, Hurtado de Mendoza commissioned another southern expedition, also led by Juan Fernandez. His ships ran into trouble and the expeditionaries were forced to stay in Chiloe, living shoulder-to-shoulder with the indigenous people.
In 1567, the process of conquering Chiloe began by order of governor Rodrigo de Quiroga. The person appointed to carry out this task was Martin Ruiz de Gamboa. His expedition, made-up of 110 well-supplied men, settled in these new lands they now owned. Ruiz de Gamboa saw it fit to found a city by the river the locals called Quilque (presently, the Gamboa river), and he christened it Santiago de Castro. He called the island Nueva Galicia. However, this name did not stick and Chiloe was maintained, which was the name used by the huilliches.
After establishing the encomienda system (a labor system that consisted on forcing the indigenous people to serve a Spanish encomendero or a king-appointed landowner, receiving no retribution for their work) and setting up the rest of the basic institutions, Ruiz de Gamboa returned to the mainland to continue fighting the war of Arauco.
After the disaster of Curalba (1598), a skirmish in which the mapuches beat the Spanish and killed Martin Oñez de Loyola, governor of Chile, Chiloe was separated from the rest of the land taken over by the Spaniards. This happened because all of the cities located between the Biobio river and the Chacao canal were either abandoned or destroyed, except for Valdivia. During the first half of the XVII century, the inhabitants of Castro suffered many attacks from Dutch corsairs that ended up destroying half the city.
Due to these assaults, the Spaniards requested on many occasions to abandon the islands because of the misery and isolation going on there; however, this never happened because, strategically, Chiloe was too important to the Spanish. In 1767, the king of Spain authorized the viceroy of Peru, Manuel de Amat, to take control of defending the archipelago and naming a new governor. He chose captain Carlos de Beranger. Nevertheless, the annexation of this land into the viceroyalty was only temporary, as it was stipulated that it was only to be for a while, until normal order was restored. The first thing Beranger did upon his arrival was found the Villa and Fuerte Real de San Carlos de Chiloe (San Carlos de Chiloe Royal Township and Fort, present-day city of Ancud). Then, in 1784, the Intendancy of Chiloe was created. It received its instructions from Lima, but five years later it became a military governance.
The revolutionary movement that began in Chile in 1810 went unnoticed in Chiloe. However, in 1813, by order of the viceroy of Peru, Jose Fernando Abascal, brigadier Antonio Pareja arrived to the archipelago to form an expedition to help restore Spanish power in the kingdom of Chile.
He had the support of the governor of Chiloe and the chilote population. When the Chiloe army was ready, it travelled to Valdivia, where it started battles with the Chilean independistas (freedom fighters), which ultimately ended in Chilean defeat at the disaster of Rancagua (1814). After this event, Chileans began the liberation of Chiloe from Spanish domain; nevertheless, the troops led by lord Thomas Cochrane were defeated by the royalists.
In 1824, 14 years after the first Government Junta (meeting), the supreme director of the Republic of Chile, Ramon Freire, once again began preparing to get rid of the Spanish once and for all. After two years of confrontations and battles, both sides agreed to sign an agreement known as the treaty of Tantauco. It was signed by the appointed commissioners of both armies at the San Antonio bridge and was ratified by Ramon Freire and Antonio Quintanilla on January 15, 1825. Its first point stated that Chiloe was to become part of the Republic of Chile.