On 12 July 1936, in Madrid, a far right group murdered Lieutenant José Castillo of the Assault Guards (a special police corps created to deal with urban violence) and a Socialist. The next day, Assault Guards with forged papers "arrested" Sotelo and abducted him in an Assault Guard van. Leftist gunman Luis Cuenca, who was operating in a commando unit of the Assault Guard led by Captain Fernando Condés Romero, is said to have murdered Sotelo. Condés was close to the Socialist leader Indalecio Prieto.
The murder of such a prominent member of parliament, with involvement of the police, aroused suspicions and strong reactions among the Center and the Right. Although the Nationalist generals were already in advanced stages of planning an uprising, the event provided a catalyst and convenient public justification for their coup.
The monarchist General José Sanjurjo was the figurehead of the rebellion, while Emilio Mola was chief planner and second in command. Mola began serious planning in the spring, but General Francisco Franco hesitated until early July, inspiring other plotters to refer to him as "Miss Canary Islands 1936". Franco was a key player because of his prestige as a former director of the military academy and as the man who suppressed the Socialist uprising of 1934.
Fearing a military coup, Prime Minister Casares Quiroga sent General Manuel Goded Llopis to the Balearic Islands and Franco to the Canary Islands. On 17 July 1936, the plotters signaled the beginning of the coup by broadcasting the code phrase, "Over all of Spain, the sky is clear."
The Nationalists (also called "insurgents", "rebels" or by opponents "Francoists" or overinclusively as "Fascists") fearing national fragmentation, opposed the separatist movements, and were chiefly defined by their anti-communism, which galvanized diverse or opposed movements like falangists or monarchists. Their leaders had a generally wealthier, more conservative, monarchist, landowning background, and they favoured the centralization of state power.
One of the Nationalists' principal stated motives was to confront the anti-clericalism of the Republican regime and to defend the Church, which had been the target of attacks, and which many on the Republican side blamed for the ills of the country. Even before the war religious buildings were burnt and clergy killed without action on the part of the Republican authorities to prevent it, and many of the massacres perpetrated by the Republican side targeted the Catholic clergy. Franco's Moroccan Muslim troops found this repulsive as well, and for the most part fought loyally and often ferociously for the Nationalists. Articles 24 and 26 of the Constitution of the Republic had banned the Jesuits, which deeply offended many within the conservatives. The revolution in the republican zone at the outset of the war, killing 7,000 clergy and thousands of lay people, drove Catholics, left then with little alternative, to the Nationalists.
Republicans (also known as Spanish loyalists) received weapons and volunteers from the Soviet Union, Mexico, the international Socialist movement and the International Brigades. The Republicans ranged from centrists who supported a moderately capitalist liberal democracy to revolutionary anarchists and communists; their power base was primarily secular and urban, but also included landless peasants, and it was particularly strong in industrial regions like Asturias and Catalonia. This faction was called variously the "loyalists" by its supporters; the "Republicans", "the Popular Front" or "the Government" by all parties; and "the reds" by its enemies.
The conservative, strongly Catholic Basque country, along with Galicia and the more left-leaning Catalonia, sought autonomy or even independence from the central government of Madrid. This option was left open by the Republican government. All these forces were gathered under the Republican Popular Army (Ejército Popular Republicano, or EPR) .
Catalan and Basque nationalists were not univocal. Left-wing Catalan nationalists were on the Republican side. Conservative Catalan nationalists were far less vocal supporting the Republican government due to the anti-clericalism and confiscations occurring in some areas controlled by the latter (some conservative Catalan nationalists like Francesc Cambó actually funded the rebel side). Basque nationalists, heralded by the conservative Basque nationalist party, were mildly supportive of the Republican government, even though Basque nationalists in Álava and Navarre sided with the uprising for the same reasons influencing Catalan conservative nationalists. Notwithstanding the religious matters, the Basque nationalists, who nearly all sided with the Republic, were, for the most part, practicing Catholics.
The Spanish Civil War had large numbers of non-Spanish citizens participating in combat and advisory positions. Foreign governments contributed large amounts of financial assistance and military aid to forces led by Franco. Forces fighting on behalf of the Republicans also received limited aid, but support was seriously hampered by the arms embargo declared by France and the UK. These embargoes were never very effective however, and France especially was accused of allowing large shipments through to the Republicans (but the accusations often came from Italy, itself heavily involved for the Nationalists). The clandestine actions of the various European powers were at the time considered to be risking another 'Great War'.
The League of Nations' reaction to the war was mostly neutral and insufficient to contain the massive importation of arms and other war resources by the fighting factions. Although a Non-Intervention Committee was created, its policies were largely ineffective. Its directives were dismantled due to the policies of appeasement of both European democratic and non-democratic powers of the late 1930s: the official Spanish government of Juan Negrín was gradually abandoned within the organization during this period.
Support for Nationalists
Despite the Irish government's prohibition against participating in the war, about 250 Irishmen went to fight for the Republicans and around 700 of Eoin O'Duffy's followers ("The Blueshirts") went to Spain to fight on Franco's side. The Nationalists received weapons and logistical support from Portugal, and Salazar sent soldiers to fight for the Nationalists in the Viriato Legion. Romanian volunteers were led by Ion I Moţa, deputy-leader of the Legion of the Archangel Michael (or Iron Guard), whose group of seven Legionaries who visited Spain in December 1936 to ally their movement to the Nationalists.
Francisco Franco asked Adolf Hitler from Nazi Germany and Benito Mussolini from Fascist Italy to aid the Nationalists. Hitler agreed and ordered three major military operations in Spain during the Spanish Civil War. He authorized Operation Feuerzauber ("Fire Magic") in late July 1936. He mobilized 20 three-motor Junker 52 planes with six escort fighters, 85 Germans on the SS Usaramo ship to work on the planes, and transferred German troops stationed in Morocco to Spain. A few months later in late September, Hitler again mobilized men and materials to aid Franco for Operation Otto. He sent 24 more Panzer I light tanks, a flak, and some radio equipment. German commander Major Alexander von Scheele also converted the Junkers 52s to bombers. By October, there were an estimated 600–800 German soldiers in Spain. Hitler’s largest and last move was the Condor Legion (Legion Condor). Initiated in November 1936, he sent an additional 3,500 troops into combat and supplied the Spanish Nationalists with 92 new planes. Hitler kept the Condor Legion in Spain until the end of the war in May 1939. At its zenith, The German force numbered about 12,000 men, and as many as 19,000 Germans fought in Spain.
After Franco’s request and in response to Adolf Hitler's encouragement, Benito Mussolini joined the war, partly because he did not want to be outdone by Hitler. While Mussolini sent more ground troops than Hitler, he initially supplied fewer materials. At the beginning of war in September 1936, Mussolini had only supplied 68 aircraft and several hundred small arms to the Nationalists. However, the Royal Italian Navy (Regia Marina Italiana) played a major role in the Mediterranean blockade and ultimately Italy supplied machine guns, artillery, aircraft, tankettes, the "Legionary Air Force" (Aviazione Legionaria), and the "Corps of Volunteer Troops" (Corpo Truppe Volontarie, or CTV). The Italian CTV reached a high of about 50,000 men and, by rotation, more than 75,000 Italians were to fight for the Nationalists in Spain.
Support for Republicans
Many non-Spanish persons, often affiliated with radical, communist or socialist parties or groups, joined the International Brigades, believing that the Spanish Republic was the front line of the war against fascism. The troops of the International Brigades represented the largest foreign contingent of those fighting for the Republicans. Roughly 30,000 foreign nationals from up to 53 nations fought in the brigades. Most of them were communists or trade unionists, and while organised by communists guided or controlled by Moscow, they were almost all individual volunteers. About 3,000 Poles volunteered for the International Brigades. American volunteers such as the Abraham Lincoln Brigade and Canadians in the Mackenzie-Papineau Battalion also fought in the International Brigades.
Over five hundred Romanians fought on the Republican side, including Romanian Communist Party members Petre Borilă and Valter Roman.
The Soviet Union primarily provided material assistance to the Republican forces. In total USSR provided Spain with 806 planes, 362 tanks, and 1,555 artillery pieces. The Soviet Union ignored the League of Nations embargo and sold arms to the Republic when few other nations would do so; thus it was the Republic's only important source of major weapons. Stalin had signed the Non-Intervention Agreement but decided to break the pact. However, unlike Hitler and Mussolini who openly violated the pact, Stalin tried to do so secretly. He created a section X of the Soviet Union military to head the operation, coined Operation X. The Republic had to pay for Soviet arms with the official gold reserves of the Bank of Spain, in an affair that would become a frequent subject Francoist propaganda afterwards.
The Soviet Union also sent a small number of military advisors to Spain. While Soviet troops amounted to no more than 700 men, Soviet "volunteers" often operated Soviet-made Republican tanks and aircraft. In addition, the Soviet Union directed Communist parties around the world to organize and recruit the International Brigades.
Unlike the United States and major Latin American governments such as those of Argentina, Brazil, Chile, and Peru, the Mexican government supported the Republicans fully and publicly (although a large part of Mexican society wanted a Nationalist victory). Mexico refused to follow the French-British non-intervention proposals, but Mexican aid meant little compared to the quantities supplied to the Nationalists by Italy and Germany. Mexico furnished $2,000,000 in aid and provided some material assistance, which included a small amount of American-made aircraft such as the Bellanca CH-300 and Spartan Zeus that served in the Mexican Air Force.
