This book provides a comprehensive exploration of Carlism and the First Carlist War in Spain, a pivotal conflict that spanned from 1833 to 1840. It delves into the ideological foundations, historical context, and key events that fueled the Carlist cause, examining how a dynastic dispute between the supporters of Carlos María Isidro and Isabella II transformed into a broader ideological struggle. The book analyzes the cultural, religious, and political dimensions of Carlism, highlighting its defense of traditional monarchy, Catholicism, and regional autonomy in contrast to the liberal, centralizing forces of the time. Through an in-depth examination of the major battles, key figures, and military strategies, the narrative provides a detailed account of the conflict's impact on Spain's political and social fabric. The legacy of Carlism extends beyond the war itself, influencing the development of Spanish conservatism, regionalism, and nationalism, as well as the continuing tensions between tradition and modernity. The Carlist vision of Spain, with its emphasis on a deeply Catholic and decentralized monarchy, persisted throughout the 19th and 20th centuries, shaping political movements and cultural debates that continue to reverberate in Spain today. This work thus situates Carlism within the broader narrative of Spanish history, exploring its lasting influence on the country's identity, politics, and culture.