John Hopkins

But it is far from a purely Francoist attack.

The planes used are exclusively German and Italian, with the Luftwaffe masterminding the whole assault.

Dropping high explosives to destroy roofs and buildings before unleashing incendiary devices to create a firestorm, they then strafe fleeing civilians with gunfire, the whole operation acting as a dress rehearsal for similar atrocities in World War II.

George Stier's eyewitness account of the aftermath is carried by news outlets across the world.

This almost unprecedented aerial attack on a civilian population provokes outrage and inspires Pablo Picasso's famous mural depicting the carnage.

The bombing crushes the ability of defenders within the town to resist the Francoist advance, and it falls at the end of April.

By the end of June, Franco is in control of the entire Basque region.

As the center of Spain's heavy industry, its loss represents an immense blow to the Republican war effort.

Though they chalk up some victories in the summer of 1937, in October Asturias, the nation's coal mining region, is conquered by Franco as well.

By now the Francoists have managed to block or impede access to all of Spain's Mediterranean ports with the help of their fascist allies.

The provision of supplies and arms to the Republicans, the latter mostly acquired through intermediaries to get around the non-intervention treaty, is now a severe logistical challenge.

With government-controlled territories bursting with refugees, sourcing enough food becomes critical.

Franco attempts to use the suffering of his countrymen to his own advantage.

Though hunger is less of an issue in the Francoist territory, his political opponents face staggering levels of violence.

It is estimated that around 100,000 members of political parties and trade unions are murdered, many of whom are buried in mass unmarked graves.

The families they leave behind are often driven into deep poverty as a result.

Violence does occur on the Republican side, though it is to a lesser extent.

Many members of the clergy, for example, are targeted as representatives of the Catholic Church that has sided with Franco.

By the winter of 1937, the Republicans have suffered huge losses and are having to rely on ever younger and older recruits.

The two warring sides fight over the city of Turwell in Aragon, a province in northeastern Spain.