The Spanish Civil War (1936–1939) broke out with a military uprising in Morocco on July 17, 1936, triggered by events in Madrid. Within days, Spain was divided in two: a "Republican" or "Loyalist" Spain consisting of the Second Spanish Republic (within which were pockets of revolutionary anarchism and Trotskyism), and a "Nationalist" Spain under the insurgent generals, and, eventually, under the leadership of General Francisco Franco.

By the summer, important tendencies of the war become clear, both in terms of atrocities on both sides and in the contrast between the Soviet Union's intermittent help to the Republican government and the committed support of Fascist Italy and Nazi Germany for the Nationalists.

In the early days of the war, over 50,000 people who were caught on the "wrong" side of the lines were assassinated or summarily executed. In these paseos ("strolls" or "walks"), as the executions were called, the victims were taken from their refuges or jails by armed people to be shot outside of town. Probably the most famous such victim was the poet and dramatist Federico García Lorca. The outbreak of the war provided an excuse for settling accounts and resolving long-standing feuds. Thus, this practice became widespread during the war in areas conquered. In most areas, even within a single given village, both sides committed assassinations.

Any hope of a quick ending to the war was dashed on July 21, the fifth day of the rebellion, when the Nationalists captured the main Spanish naval base at Ferrol in northwestern Spain. This encouraged the fascist and other sympathetic regimes of Europe to help Franco, who had already contacted the governments of Germany and Italy the day before. On July 26, the future Axis powers cast their lot with the Nationalists. German assistance, channeled through Franco rather than to the Nationalists in general, consolidated his leadership position of the insurgency.

In the north, a rebel force under Colonel Beorlegui, sent by General Emilio Mola, advanced on Gipuzkoa. On September 5, after heavy fighting, it took Irún, closing the French border to the Republicans. On September 13 the Basques surrendered San Sebastián to the Nationalists, who then advanced toward their capital, Bilbao, but were stopped at the border of the province. The capture of Gipuzkoa had isolated the Republican provinces in the north.

Nationalist forces under Franco won a great symbolic victory on September 27 when they relieved the besieged Alcázar at Toledo. Two days after relieving the siege, Franco proclaimed himself Generalísimo and Caudillo ("chieftain"); he would forcibly unify the various Falangist and Royalist elements of the Nationalist cause.

In October, the Nationalists launched a major offensive toward Madrid, reaching it in early November and launching a major assault on the city on November 8. The Republican government was forced to shift from Madrid to Valencia, out of the combat zone, on November 6. However, the Nationalists' attack on the capital was repulsed in fierce fighting between November 8 and 23. A contributory factor in the successful Republican defence was the arrival of the International Brigades, though only around 3,000 of them participated in the battle. Having failed to take the capital, Franco bombarded it from the air and, in the following two years, mounted several offensives to try to encircle Madrid.

On November 18, Germany and Italy officially recognized the Franco regime, and on December 23, Italy sent "volunteers" of its own to fight for the Nationalists.

Detailed chronology: 1936

February 16 Popular Front electoral victory.

July

July 12 In Madrid, Lieutenant José Castillo of the Guardia de Asalto is murdered by four falangist gunmen who awaited the recently married lieutenant in the afternoon hours in front of his house. He was a member of the Unión Militar Republicana Antifascista, an anti-fascist organization for military members, and also helped to train socialist militia. July 13 In retaliation, around 3am, José Calvo Sotelo, leader of the right-wing monarchist party, is murdered by police officers. Only a few hours after the assassination of Castillo, his close friend Police Captain Fernando Condés and other police officers arrest Calvo Sotelo in his house. Paul Preston has speculated that the police officers may have acted of their own accord. This was a factor in the uprising of 18 July, though the Nationalist revolt had been in planning for months.Beevor, Antony; "The Battle for Spain" Driving with him in a police car of the Guardia de Asalto, Officer Luis Cuenca shot him in the back of the neck in summary execution. July 14 Shootout between the Guardia de Asalto and falangist militias in the streets surrounding the cemetery of Madrid, where the burials of José Castillo and Calvo Sotelo are taking place. Four people killed. July 17 Army uprising in Morocco. Military uprising of the Spanish Legion in Morocco. General , commanding officer of the East Army, is murdered by rebels, who also imprisoned commanding General Gomez in the late afternoon. Loyal police troops from the Guardia Civil and Guardia de Asalto hold the cities Tetouan and Larache, but come under heavy attack by the rebels. General Franco orders the killing of his own nephew, a major in Tétouan, for staying loyal to the government. By late evening, all of Morocco is in the hands of the rebels. From the Canary Islands, Franco declares a "state of war" for all of Spain. Prime Minister Santiago Casares Quiroga spends the whole day telephoning different regional military administrations to clarify the situation. Pamplona, Zaragoza, Oviedo, Salamanca, Ávila, Segovia, and Cádiz are already in rebel hands. July 18 The rebels gain control over about one third of Spain. July 19 Franco flies from the Canary Islands to Tétouan and takes command of the army in Africa.Casares Quiroga resigns as chief of the Republican government.Diego Martínez Barrio tries to form a new government, but cannot obtain broad enough parliamentary support.José Giral forms a government, which orders that arms be issued to the general populace.Seville, one of the most important cities in the south, is unsuccessfully defended by local police troops and a poorly armed workers' militia. While the heaviest weapons police possess are machine guns, the rebel General Gonzalo Queipo de Llano sends in artillery and heavily armed troops. Seville falls to the rebels.This is the day the People's Olympiad was scheduled to open in Barcelona, as a protest against the official 1936 Summer Olympics in Berlin, the capital of Nazi Germany. The games have now been cancelled due to the war.In Barcelona, heavy street-fighting breaks out between police, workers militias and loyal troops on one side and around 12,000 rebel soldiers on the other. After it becomes obvious that Civil Guard, Guardia de Asalto and City Police would not be enough to keep control of the city, the Generalitat (regional government of Catalonia), decide belatedly to arm loyal civilians. July 20 Rebels defeated in Madrid and Barcelona, but they take Mallorca. In Madrid, around 10,000 citizens, among them police officers and soldiers, attack the Montaña Barracks, held by rebel General Fanjul and around 2500 soldiers. Some soldiers in the Barracks want to surrender and wave a white flag. The crowd moves towards the barracks, while the soldiers who wanted to surrender are overwhelmed by the rebels. The rebels then immediately fire heavy machine guns and throw hand grenades into the masses, leaving many wounded or dead. The crowd storms the barracks and massacres the defenders. General Fanjul is among the few captured alive.Barcelona: The combined forces of local police troops, workers' militias and citizens gain back control over the city in a dramatic two-day barricade fight.Mallorca: After heavy resistance, especially at the air base, the rebels gain control over Mallorca.The official leader of the uprising, General José Sanjurjo, dies in an air accident in a small aircraft bringing him back to Spain from his exile in Portugal. He had insisted, against the advice of the pilot, on taking all of his possessions with him. The overloaded aircraft crashed taking off. July 21 Start of the Siege of the Alcázar de Toledo.The Nationalist insurgents have control of the Spanish zones of Morocco, the Canary Islands, the Balearic Islands except Menorca, the part of Spain north of the Sierra de Guadarrama and the Ebro (except Asturias, Cantabria, the north of the Basque Country, and Catalonia). Among the major cities, the insurgents hold Seville, but the Republicans retain Madrid and Barcelona.Toledo: After three days of street battles against forces loyal to the government, about 1000 Civil and Assault Guards, falangists and a handful of infantry cadets, under the leadership of Colonel José Moscardó Ituarte, retreat into the Alcázar of Toledo, a stone fortress set on high ground overlooking the Tagus and the city. They take with them their own families, plus a few hundred women and children as hostages, most of them families of well-known leftists. July 22 Vallehermoso, Santa Cruz de Tenerife in la Gomera, a village of 4000, is the last place in the Canary Islands to fall to the rebels. Police Officer Francisco Mas García organized the hopeless resistance. The actual battle for the town lasted several hours. The councilor, the police officers and the leader of the local workers' council were condemned to death. In the hour before his execution, police chief Don Antonio wrote to his wife: "I die calm, because I believe in the justice of God".The navy and air force remain loyal to the government. Thanks to the initiative of noncommissioned officer Benjamin Balboa, most of the Navy stayed loyal to the Republic. He was on duty in the central military radio station. As soon as he got notice of the uprising he informed the Naval Ministry and arrested his commanding officer, Captain Castor Ibáñez, then spent the night informing navy ships about the uprising. The sailors on the ships formed councils and gained control of the ships, despite heavy resistance from the officers. Spain lost three quarters of its navy officers that night, but the Navy was saved for the Republic. The officers of the Spanish Air Force are traditionally very Republican, but the air force has only a few obsolete planes. July 23 The Nationalists declare a government in the form of the National Defense Council, which meets for the first time in Burgos. July 24 Start of French aid to the Republican side. For the moment, the help only involves sending a handful of obsolete aircraft for the Spanish Republican Air Force, but the very fact that France seems willing to help is eminently morally important for the supporters of the Republic.The Durruti Column, around three thousand men, mostly workers, led by Buenaventura Durruti are the first volunteer militia to leave Barcelona, heading for the Aragon front. July 28 First arrival of German and Italian planes in aid of the Nationalist side. In the world's first major military airlift, German and Italian planes transport troops from Morocco to Spain, bypassing the naval blockade. July 31 Great Britain bans sale of arms to the Spanish Republic.

August The social revolution, collectivizations. (See Spanish Revolution of 1936)