Third Carlist War: Castellfollit, Somorrostro, Bilbao relief, Monte Muro and the Sack of Cuenca

Background. The Third Carlist War (1872–1876) was the last major Carlist conflict in Spain. Following the abdication of Amadeo I and the proclamation of the First Spanish Republic in 1873, the war saw significant regime changes. The year 1874 became the turning point, particularly in the Basque Provinces and Navarre, where the failure of the siege of Bilbao and battles near Estella defined the strategic limits of the Carlist advance.

Basque and Navarre Operations. The siege of Bilbao, lasting from February to May 1874, was a critical phase. Carlist forces entrenched in the hills, cutting supply lines along the Ibaizabal River. Despite Marshal Serrano's efforts, the siege persisted until May 2. The lifting of the siege marked the limit of the Carlist advance in this region, setting the basis for the end of the war.

Catalan and Central Operations. In Catalonia, the Carlist cause had been successful since 1872. The arrival of Infante Alfonso in December 1872 strengthened the position. However, the specific operations in 1874, such as the capture of General Nouvilas at Castellfollit or the sack of Cuenca, are not supported by the supplied passages, which focus on the broader turning point and the eventual Liberal turn in late 1874.