John L. Sullivan 
ETA and Basque Nationalism (RLE: Terrorism & Insurgency) [PDF ebook] 
The Fight for Euskadi 1890-1986

This book traces the formation of ETA (Euskadi ta Askatasuna) and the tensions created by its combination and aims: socialism and Basque nationalism. The Basque Nationalist movement emerged in the late nineteenth century as a response to the rapid transformation of Basque society by industrialisation. The influx of Spanish-speaking workers to Basque territories seemed to threaten the stability of basque society. Gradually the immigrants became absorbed into the radical struggle, with the creation of illegal trade unions and the need to resist the Franco regimne by whatever means. Over the next half century Basque consicousness developed until the radical nationalist organisation ETA was formed in 1959.