In 1937, the Nationalists, under the leadership of Francisco Franco began to establish their dominance. An important element of support was their greater access to foreign aid, with their German and Italian allies helping considerably. This came just as the French ceased aid to the Republicans, who continued, however, to be able to buy arms from the Soviet Union. The Republican side suffered from serious divisions among the various Communist and anarchist groupings within it, and the Communists undermined much of the anarchists' organisation.
With his ranks swelled by Italian troops (the Corpo Truppe Volontari) and colonial troops from Spanish Morocco, Franco made additional attempts to capture Madrid in January and February 1937, but failed again.
On February 21 the League of Nations Non-Intervention Committee ban on foreign volunteers went into effect. The large city of Málaga was taken on February 8. On April 26, the German Condor Legion bombed the town of Guernica (Gernika) in the Basque Country; two days later, Nationalist General Emilio Mola's men entered the town.
After the fall of Guernica, the Republican government began to fight back with increasing effectiveness. In July, they made a move to recapture Segovia, forcing Franco to pull troops away from the Madrid front to halt their advance. Mola, Franco's second-in-command, died in a plane crash on June 3. Bilbao fell to the Nationalists in June. In early July, the Republicans counterattacked west of Madrid. The Nationalists repulsed this attack with some difficulty in the Battle of Brunete.
Franco soon regained momentum, invading Aragon in August and then taking the city of Santander (now in Cantabria). On August 28, the Vatican recognized the Franco government. Two months of bitter fighting followed and, despite determined Asturian resistance, Gijón fell in late October, effectively ending the war in the North. At the end of November, with the Nationalists closing in on Valencia, the government moved again, from Valencia to Barcelona.
Detailed chronology
January–March January 5 Nationalist General Orgaz with 18,000 men attacks the roads northwest of Madrid in an attempt to cut the city's supply lines. Madrid suffers several air raids daily, and sometimes nighttime raids as well.
January 6 Nationalists take Boadilla del Monte. The International Brigades (IBs) defended the town; one of the few survivors of the Internationals is Esmond Romilly, 18-year-old nephew of Winston Churchill. Romilly volunteered despite his famous uncle's open sympathy for Franco, like that of most of his colleagues in the ruling British Conservative Party.
January 11 The Nationalist offensive northwest of Madrid is stopped. Both sides, temporarily exhausted after heavy casualties, start to build trenches and dig themselves in.
January 17 The Nationalists begin the battle to take Málaga. Three Nationalist columns converge on the city from Sevilla and Granada.
January 19 General Enrique Líster with the IBs gains back the Cerro de los Ángeles next to Madrid. This hill overlooks the city; the heavy Nationalist artillery there had been shelling the city. The IBs become more and more the key units in the Spanish Republican Army.
February 5 A Nationalist army approaches Málaga. The situation in Málaga epitomizes the worst conditions existing in the Republican zone: perhaps 600 hostages are held on a prison ship in the harbor, and groups of them are shot in reprisal for the air raids over the port. The sailors' committees in the fleet and the city administration are divided in mortal rivalry between the CNT and the Communist Party of Spain. Like all Republican cities, there is no anti-aircraft defense. Its militiamen, mostly anarchists, and not yet reorganized into the new Popular Army, built no trenches or roadblocks, because they consider this cowardice. The government assigns Colonel Villalba, a professional officer, to organize the defense, but without guns to place on the heights, without ammunition to give his soldiers, and without the slightest possibility of controlling the rivalries within the city, there is virtually nothing he can do. The invading force consists of some 10,000 Moroccans, 5,000 Requetés (right-wing militiamen), and 5,000 Italians, with plentiful supplies of trucks and artillery. They have only a few tanks and planes, but they can use these with maximum effectiveness in the virtual absence of effective deterrents.
February 6 Nationalists start a powerful offensive in the Jarama Valley. Nationalist General Orgaz is in command of around 40,000 troops, most of them Spanish Foreign Legion and Moroccan cavalry, supported by anti-tank artillery, two battalions of German-operated heavy machine guns (German ground troops under the command of the Condor Legion), German-operated tanks and planes (Condor Legion), and 600 Irish Blueshirts under the command of the right-wing Eoin O'Duffy. The Nationalists want to cut the main Madrid-Valencia highway. General Pozas, commander of the new Central Army of the Republic, is planning his own offensive against the Nationalist line and is therefore massing men and material in the same area. Due to their own planned offensive, the Republicans fail to fortify their high ground, and the Nationalist offensive takes them completely by surprise. The hills are quickly lost, as are the two principal bridges. The Republican guards on the bridges are killed in the night by Moroccan commandos. The guards on the Pindoque Bridge manage to mine the bridge during the attack, but it remains usable for enemy tanks and trucks. Citizens flee Málaga. About 100,000 people begin a disorganized mass exodus along the coastal road to Almería. The road is blocked by slow vehicles and wounded people; for the next two weeks, the Nationalist air force and navy bomb the road at will. German warships of the Non-Intervention Committee participate in the shelling, sometimes in the presence of Royal Navy vessels which do nothing to intervene (until the 1960s, truck drivers continued to find skeletons of those who fled Málaga in February 1937).
February 8 Málaga taken by Franco's troops. The militiamen resisted rifle and grenade fire, but broke at the totally unfamiliar sight of tanks. The Nationalists start immediately to take an enormous number of prisoners and to execute them. For example, participation in a strike several years previously is grounds for execution. The Italian military authorities are horrified at the number of executions and the mutilations practiced on the corpses and those who were wounded, as well as the mass rape of women. Nationalists advance in the Jarama Valley. Soviet tanks slow down the advance for brief periods, but the Nationalists quickly concentrate heavy artillery fire and force their withdrawal. The planes of the Condor Legion control the air.
February 10 The XIV and XV IBs fortify the Republican army in the Jarama. The troops stop the Nationalist advance, but take horrible losses in doing so. At one point the Nationalists force approximately 30 survivors of a captured British machine gun group to advance in front of their attack; half of these men die under fire of their own comrades.
February 12 Air supremacy for the Republic at the Jarama front, all-out attack on the last Republican positions. 40 new Soviet airplanes arrive at the Jarama front, giving the Republic air supremacy in the area. These planes consist of 15 ground strafers and 25 Polikarpov I-15 fighters; the fighters are nicknamed "Chatos". The arrival of these planes forces the enemy planes to retreat. On the night of February 12, Nationalist General Orgaz commits all his reserves to gain control over the last key positions that still prevent his forces from cutting the Valencia highway. Several companies of the IBs — including British and Polish — as well as Spanish companies, were "cut to pieces" attempting to hold these positions. February 15 The force of the offensive in the Jarama had spent itself. As in the Battle of the Corunna Road, the Nationalists have gained ground, but strategic victory had escaped them. The Foreign Legion is broken. Around 20,000 men died in the 10 days of the Jarama Battle, two thirds of them Republicans.
February 17 The anarchist writer Pedro Orobon dies in an air raid at Madrid.
February 21 Republican General José Asensio Torrado dismissed, after the fall of Málaga.The Non-Intervention Committee's ban on foreign national and stateless "volunteers" went into effect.
February 27 The newly formed Abraham Lincoln Battalion, part of the IBs, consisting mostly of North Americans, had arrived at the Jarama front February 13; they are ordered to carry out a suicidal attack. 127 men die and more than 200 are wounded. Responsibility for poorly planned attack lies on Brigade Commander Copic, who refuses to see the wounded leader of the "Lincolns", Robert Hale Merriman, after the disastrous failed action.
March 5 First council of the PCE (Communist Party of Spain) in the war. The PCE makes a declaration in favor of democracy and against revolution and Trotskyism. The delegates sharply attack the government and the CNT.
March 8 Strong Nationalist attack in the Guadalajara starts at 7 a.m. Italian troops quickly break the front and, by the end of the day, dominate the heights, from which they can "roll" downhill to Madrid. Their plan is to advance to Madrid via Brihuega and Guadalajara. The attacking force includes 250 tanks, 180 pieces of artillery, 4 motorized machine gun companies, about 70 planes, and a large number of trucks.
March 9–March 11 The Italians are moving too rapidly for their units to preserve communications and supply lines. A sudden turn in the weather catches the Italian trucks in a snow and sleet storm, just as the Republicans begin to hold firm south of Brihuega and Trijueque. While the Italian planes are grounded by the weather, the Republican air force is operating at considerable risk from airfields outside of the bad weather zone. Low-flying fighters are machine-gunning the stalled truck columns while vintage 1918 Breguets, which had survived the summer air battles, run bombing missions. Vittorio Vidali and Luigi Longo, the political leaders of the IB Garibaldi battalion (Italian volunteers on the Republican side), mount a propaganda campaign intended to destroy the morale of the CTV, pulling loudspeakers up to the lines and dropping leaflets from the air, exhorting the Italian soldiers not to shoot against their brother workers and to leave the Fascists.
March 12 The Republican forces start a massive counterattack, with the support of 70 Soviet tanks and strong air cover. The CTV has no AA artillery, and it suffers heavily from air attack; most casualties belong to XI Gruppo de Banderas, whose commander (Console Liuzzi) is killed.
March 13 Improving weather allows the Italian planes to cover the withdrawal of Division III "Penne Nere" from the Trijueque sector, and the battle is more or less stabilized.
March 18 Republican divisions under Cipriano Mera and Enrique Líster with 60 T-26 tanks of the Pavlov Brigade take back Brihuega, causing the collapse of the Italian front and the rout of Division I "Dio lo Vuole", which in turn forces Division IV "Littorio" to abandon its positions. The rout is not stemmed until the morning of next day.