Hywel Frances examines primary sources to explore the reasons that led many Welsh miners to volunteer for the International Brigades and thus to fight in the Spanish Civil War. Welsh miners made up one of the largest contingents within the British Battalion of the International Brigades in the Spanish Civil War. Coming from the valleys all across South Wales, they brought with them a political tradition unique in Britain, with a in its combination of trade union militancy, radical extra-parliamentary activity and internationalism. Hywel Francis draws on a wide variety of contemporary sources to paint a vivid picture of the tumultuous politics of South Wales in the 1920s and 1930s -– the context for the decision made by so many to volunteer. The book describes the process of volunteering, the militant role played by the Welsh volunteers, and the mass movements of political solidarity with Spain within Wales. It also includes many illustrations, and reproduces letters written by volunteers to their relatives and friends back in Wales.