These soldiers are Carlists as indicated by their prominent red berets, which became (and are) icons of the Carlists in Spain. The Carlists are an ultra-conservative popular political movement in Spain. They take their name from Carlos V, son of Ferdinand VII, who was a pretender to the throne of Spain with his declaration to be rightful heir on October 1, 1833. Politically, the Carlists advocated for a monarchical form of government modeled on the late-fifteenth century reign of Ferdinand and Isabel, who shared their power with the regional governments of Spain's various kingdoms on the Iberian Peninsula. In addition, the Carlists supported the Salic Law enacted by Felipe V (r. 1700-1746), which reformed the process of succession in Spain such that only male heirs could inherit the throne and female heirs only in the absence of a male heir on any royal line.
Although they historically rejected a strong centralized government in favor of greater regional power, the Carlists allied with Franco and the Nationalists during the Spanish Civil War. Since 1931, the Carlists had been cooperating with right-wing Catholic movements in Spain to resist the spread of Republican legislation. Manual Fal Conde became head of the movement in 1934 and, thus, began a period when the Carlists became more organized and took on a paramilitary character. They even developed their own plots to overthrow the Republican government. With such ideas, many Carlists made contact with other disaffected conservative groups and monarchists. In particular, General Mola, a central figure in the Nationalist uprising of July 1936, ensured the Requetés, Carlist militias, were involved in the military action of Nationalist Spain. Throughout the war, these militias accepted somewhere between 70,000 and 100,000 volunteers into their ranks.
Practically and at the local level, many Carlists had no difficulty allying with right-wing groups, even those of the fascist persuasion, against the common enemies of republicanism and socialism. Yet, in terms of the ideological orientation of the group, the Carlists were often divided. Purists, like Fal Conde, hoped for a Carlist uprising that would eventually install a government amenable to its goal of restored decentralized monarchy. Other Carlists were more flexible and many viewed the emergence of a strong state, as the fascists ultimately realized, as a necessary step to purify Spain and bring about a decentralized Carlist utopia. In spite of these differences and Franco's eventual exiling of Fal Conde to Portugal, the Carlist remained a vital part of the Nationalist effort against Republican Spain especially during the early years of the war.
Arlaiz is the artist of this poster. He designed other posters for the Carlists, such as a recruiting poster, which were equally sparse in terms of text. Other than that, little is known about Arlaiz.