International Brigades

The International Brigades were volunteer military units formed to support the Popular Front government of the Second Spanish Republic during the Spanish Civil War. Organised under the auspices of the Communist International (Comintern), they operated from 1936 until their dissolution in 1938. Comprising an estimated 32,000 foreign volunteers over the course of the conflict, the brigades came to symbolise international anti-fascist solidarity at a time when most Western democracies adhered to strict non-intervention policies. Their legacy extends beyond the war itself, with the term sometimes applied more broadly to foreign volunteer units fighting in the armed forces of other states.

Formation and Recruitment

The idea of recruiting foreign volunteers to defend the Spanish Republic emerged in the early months of the war. Although initially proposed informally in August 1936, the plan gained momentum when the Comintern authorised recruitment following confirmation that the Western democracies would not supply military assistance. The main organisational structures were put in place in Paris under the supervision of Soviet personnel, most notably Colonel Karol Świerczewski. Political figures including Luigi Longo and Willi Münzenberg played key roles in coordinating recruitment, logistics, and propaganda.
Volunteers arrived from a wide range of countries, with particularly large contingents from France, Italy, Germany, the United States, Poland, Britain, and the nations of Latin America. Many were motivated by anti-fascist conviction, while others hoped that victory in Spain might influence political change in their own homelands. Conditions of service were informal; there were no contractual terms or defined periods of enlistment, complicating later attempts to manage discipline and rotation.
Entry into Spain was achieved by train or ship via France, though many individuals travelled independently. Volunteers converged at Albacete, which became the central training base and headquarters of the organisation. Leadership was dominated by Comintern officers and experienced Communist exiles, including André Marty, Luigi Longo, and Giuseppe Di Vittorio. Several hundred military veterans—many exiled after the First World War—were sent from the Soviet Union to provide technical and tactical expertise.

Organisation and Structure

The brigades were incorporated into the structure of the Spanish Republican Army as mixed brigades, with battalions often composed of volunteers sharing common language or national background. Discipline was strict, particularly in the early phases when extended periods of training were required to mould disparate volunteers into cohesive fighting units. Political commissars were assigned to ensure ideological reliability and maintain morale in difficult conditions.
Jewish volunteers were notably numerous, forming a substantial proportion of the brigades’ membership. A distinct Jewish company was created within the Polish battalion and named after Naftali Botwin. In addition to national contingents, there were also groups of intellectuals, writers, and political activists whose memoirs later provided vivid records of their experiences.

Major Engagements

The International Brigades took part in many of the major battles of the Spanish Civil War. Their early arrival coincided with the defence of Madrid in November 1936. Though they constituted only a small fraction of the Republican forces present, their determined resistance provided a significant moral boost to both troops and civilians. Comintern propaganda magnified their role, leading foreign observers to overestimate the extent of their involvement.
Subsequent engagements included:

• Battle of Jarama (1937): A protracted and costly effort to halt Nationalist attempts to cut the Madrid–Valencia road.
• Battle of Guadalajara (1937): A rare Republican victory, largely against Italian forces, in which the brigades played an important supporting role.
• Battle of Brunete (1937): An ambitious offensive west of Madrid that ultimately failed to achieve its strategic aims.
• Battle of Belchite (1937): Part of a wider Aragon campaign that inflicted heavy casualties on the brigades.
• Battle of Teruel (1937–38): A brutal winter battle, initially successful for the Republic but later reversed.
• Aragon Offensive (1938): A major Nationalist attack that inflicted severe losses on Republican international units.
• Battle of the Ebro (1938): The last major Republican offensive, prolonged and costly, marking the final phase of effective brigade involvement.

Despite isolated successes, most campaigns ended in defeat, reflecting the wider strategic decline of Republican forces.

Political Context and Internal Divisions

The brigades were closely aligned with Soviet support for the Republic. Their presence demonstrated the USSR’s commitment to countering the aid supplied by Germany, Italy, and Portugal to the Nationalist faction. However, their strong connection to Communist structures created tensions within the broader Republican coalition. Volunteers opposed to Stalinism chose instead to join organisations such as the Workers’ Party of Marxist Unification (POUM) or anarchist militias like the Durruti Column.
Relations with anarchist groups were often strained. At the outbreak of recruitment, anarchists controlling the French border attempted to prevent the passage of Communist volunteers, but political pressure eventually secured their cooperation.

Decline and Dissolution

By 1938, the military situation for the Republic had deteriorated significantly, and diplomatic isolation persisted. In an effort to demonstrate compliance with the Non-Intervention Committee and to encourage support from liberal democracies, Spanish Prime Minister Juan Negrín announced the withdrawal of all foreign volunteers from the front. On 23 September 1938, the International Brigades were formally dissolved, though some volunteers remained in Spain in various capacities until the war’s end.
The decision did little to alter international attitudes, and Nationalist forces continued to receive covert and overt support from their European allies. As the Republic collapsed in early 1939, surviving brigadiers fled or were interned, with many later participating in resistance movements during the Second World War.