The game ended in the first week of July 1937 with a major victory when the Nationalists captured Valencia. Here is a summary of the action.
For the 9 months to March 1937, there was sporadic fighting in the North, with the Nationalists chipping away gradually at Republican territory. During this period, Mola made two major attacks against San Sebastián without success. Up to the end of 1936, there was little change in territory, with the Nationalists only making minor gains.
In early Spring of 1937, the Republicans launched an offensive in the west, occupying El Ferrol and threatening La Corruna. Meanwhile, in the east, Mola led another unsuccessful attack against San Sebastián. Mola was killed in action and his army was forced to retreat.
From April to July 1937, Nationalists forces launched a series of offensives all along the front. By early July, they had captured El Ferrol (west), Gijon (west) and San Sebastián (east).
In early July 1937, only Bilbao, Santander and surrounding regions remained in Republican hands.
During the whole period of the war, there was very little activity on the Aragon/Catalonia front with both forces staying on the defensive. The only region to change hands was Alcaniz. In early July 1937, the whole of Catalonia still remained in Rebublican hands.
The Republicans invaded the Manacor region in Mallorca, but failed to attack Palma. The Nationalist garrison attacked the invading forces three times, but failed to drive the enemy off the island. In July 1937, the Republicans still controlled Manacor, albeit with depleted forces.
SOUTH AND EAST (July to December 1936)
Initially, the Nationalist forces in the south concentrated on consolidating their position. Using reinforcements from Africa, they linked up their forces in Seville, Cordoba, Algeciras and Cadiz, pushing east where possible. By the end of September 1936, Nationalist forces had relieved Granada and captured Huelva, Malaga and Jaen.
In October 1936, General Franco split his forces in two. The 1st army, under Franco himself moved North towards central Spain, while a second army moved east along the southern coast. By the time the winter snows arrived in December 1936, the advancing Nationalists had captured Almeria on the south coast and Ciudad Real in central Spain.
Meanwhile, in the east of Spain, a smaller Nationalist force captured Badajoz and the territory around the Portuguese border, including the rail line that linked Nationalists controlled territory in north and south Spain. By early 1937, the Nationalists could move troops by rail between its north and south controlled regions.
On the Madrid front, the Nationalist General Saliquet massed troops around Segovia, remaining in defensive positions until Spring 1937. Initially, they were intended to pin Republican troops in Madrid and counter any attack northwards the Republicans may make. Later, Saliquet's troops would be used in the Assualt on the capital.
CENTRAL SPAIN (January to July 1937)
After the winter snows cleared, Franco renewed his advance northwards, capturing Toledo and reaching the outskirts of Madrid. Franco decided to bypass the republican controlled regions to the west and south-west of Madrid, judging them not to have any strategic importance.
In March/April, Franco attacked Madrid from the south while General Saliquet attacked from the north. The Nationalists had roughly 25,000 men against about 20,000 Republican defenders. After fierce resistance from Republican forces, Franco was able to drive them from the city. Madrid was at last in Nationalist hands.
In April/May the Republicans launched a ferocious counter-attack against Madrid, but were unable to recapture the city. After suffering heavy losses, the Republicans withdrew eastwards to Guadlajara.
After allowing his troops to rest a short time, Franco launched a further offensive against the Republicans in Guadlajara, determined to drive them further from the capital. By the time Valencia fell to Natinalist forces in early July 1937, Franco had driven the remnants of the Republican army back to Cuenca (only 200km from Valencia).
THE SOUTH (January to July 1937)
While Franco advanced north, the second Nationalist army under General Queipo advanced along the southern coast. By the end of Spring 1937, Queipo had captured Cartagena and Murcia. With Republican forces outnumbered and out-gunned, Quiepo pushed on to capture Alicante and Albacete by May/June 1937.
In late June 1937, Queipo attacked the strategically important port of Sevilla, capturing it in the first week of July 1937. With the fall of Madrid and Valencia, the central Republican government collapsed. The Nationalists had all but won the civil war.
Apart from the offensives in the North, Mallorca and Madrid, there was very little offensive action by the Republic. But there were a few minor incursions.
In late 1936, the Republic sent a sizeable force of militia towards Malaga. This was cut off by advancing Nationalist forces and destroyed in early 2017 after a series of battles.
In Spring 1937, a small Republican force attacked towards Toledo, but was driven off by African troops.
In July 1937, a small Republican force attacked Cuidad Real. The city was still under siege at the fall of Valencia.
After a failed attack by Nationalist forces against Santander in Spring 1937, Republican forces counter-attacked, cut-off and destroyed the attacking Nationalist army. This was probably the greatest Nationalist loss in the war.
I attach an image of the closing position.