The Republicans ranged from centrists who supported a moderately capitalist liberal democracy to revolutionary anarchists and socialists; 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.
The conservative, strongly Catholic Basque Country, along with Catalonia and Galicia, sought autonomy or even independence from the central government of Madrid. This option was left open by the Republican government.
Violent attacks by Republican forces on clergy, laity, and property of the Roman Catholic Church led the Nationalist side to call the Spanish Civil War a modern-day Crusade.The Nationalists on the contrary opposed these separatist movements. The Francoists (Nationalists) had a generally wealthier, more conservative base of support with Catholic, monarchist, centralist, landowning and fascist interests, and they favoured the centralization of state power. Most Roman Catholic clergy supported the Nationalists.
Atrocities were committed on both sides during the war. Some, including the use of terror tactics against civilians, foreshadowed World War II, as did some of the military tactics. However, while atrocities in the Republican side were committed by uncontrolled groups of radical militants against the Church or by the Stalinist NKVD (which also carried out murders of pro-Republican people, see Andreu Nin) against political enemies, on the Nationalist side these atrocities were ordered by the fascist authorities themselves in order to eradicate any trace of leftism in Spain. This included the aerial bombing of cities or the massive killings of civilians in the liberated cities.
While the war lasted only about three years, the political situation had already been violent for several years before. The number of casualties is disputed; estimates generally suggest that between 500,000 and 1 million people were killed.
The war started with military uprisings throughout Spain and its colonies. Republican sympathizers, soldiers and civilians, formally acting independently of the state, massacred Catholic clergy and burned down churches, monasteries and convents and other symbols of the Spanish Catholic Church which Republicans (especially the anarchists and communists) viewed as an oppressive institution supportive of the old order. The Republicans also attacked nobility, former landowners, rich farmers and industrialists.
During and after the war, the Nationalists carried out a program of mass-killing of opponents: unwanted individuals, including many non-combatants, were often jailed or, in many cases, killed by a firing squad. Trade-unionists, known Republican sympathisers and critics of Franco's regime were among the first to be targeted. The Nationalists also carried out aerial bombardment of civilian areas with strong assistance from the German and Italian air forces.
The impact of the war was massive: the Spanish economy took decades to recover. The political and emotional repercussions of the war reverberated far beyond the boundaries of Spain and sparked passion among international intellectual and political communities, passions that still are present in Spanish politics today.
Republican sympathizers proclaimed it as a struggle between "tyranny and democracy", or "fascism and liberty", and many non-Spanish young, committed reformers and revolutionaries joined the International Brigades, believing the Spanish Republic was the front line of the war against fascism. Franco's supporters, however, portrayed it as a battle between the "red hordes" of communism and anarchism on the one hand and "Christian civilization" on the other.
The Fascist Germany aerial bombardments in support of the Nationalists became the subject of Pablo Picasso's Guernica, symbolizing the senselessness and inhumanity of the fighting provocated by violent extremism overruning the country, resulting in significant loss of innocent life.
Pablo Picasso's Guernica:
Who would you have fought for?