The third Carlist war took place when the Carlist forces rejected the proclamation of Amadeus of Savoy as king, the first non-Bourbon monarch, who ascended as Amadeus I. The carlist pact with the republicans. In 1872 several carlist troops enter Spain through France as the pretenders entourage and began uprisings in the Basque Country and Navarre. But the insurrection ended two days later when General Moriones attacked taking the carlist forces by surprise. They signed the Amorobieta Covenant on the same day.
The covenant was soon rejected by both factions
The war didn't begin until the second half of 1872 when the pretender to the throne, Carlos, duke of Madrid, a Bourbon who proclaimed himself ‘Carlos VII’, acknowledged Catalonia’s privileges. Movements then sprang up in Basque provinces. During the first months of 1873 several Carlist campaigns took place. A few important victories gave encouragement to Carlist forces in the Basque Country. Carlos travels to Spain in the same year.
In August the Carlists made Estella in Navarre their capital after taking the city over. They also attempted to take Bilbao through a siege but failed. By September they occupied most of the Basque Country except for the capital cities and a true Carlist state was established which included a government, court, justice, military academies and even their own currency. This estate was established as a federal one.
The pretender restored the controversial jurisdiction privileges that had been abolished by Felipe V. In the meanwhile King Amadeus I resigned, because of the continuing difficulties and conflicts which plagued his short reign. There was also a group called "Alfonsinos" whose aim was to restore the Bourbons and crown Isabella II's son, Alfonso. His own supporters were divided within the context of the Third Carlist War.
After a Congress General Assembly that included the senate a new form of Government was formed and Spain was declared a Republic. The pretender gained additional support with the new republic as many of Isabella's supporters switched sides
The Carlists forces took over several cities in Catalonia , but they were defeated in 1875 by Martinez Campós' forces. On December 1874, Alfonso XII, Isabella's son, was proclaimed king, but carlists continue to hold the Basque Country and Navarre. The Spanish immersion in the Third Carlist War was continuing.
The government troops moved over 80,000 men in and planned a strategy that would tire out the carlist forces and smother the Basque-Navarre economy. But the war didn't end until 1876 when Estella was conquered by the government's regiment. Carlos was forced flee to France