Many people on both sides actively welcomed the coming conflict, certain that their faction would win the day. Agitators on both sides poured fuel on the various conflicts during the 20th century and planned for victory over their opposition. There were marches, parades, strikes, and more. Paul Preston describes the process of the erosion of moderates and the center as being one of "polarization and radicalization" and I think his description is apt. The center lost its voice and power while the extremes gained in power and prestige. The result was that many within the factions that would later be known as the Republicans and Nationalists welcomed the outbreak of war.

The Falange perhaps planned for the armed nature of the conflict most directly. Though they were relatively small in number, their gun ownership rate was quite high. This gave them a disproportionate amount of power in the days immediately following the uprising. With that said, many groups on the left also acted very quickly to enact their own plans--some of them violently.

So, yes, the Spanish Civil War was foreseen--and even welcomed--by many.

The Second Republic was never particularly stable, but in the 2-3 years immediately preceding the outbreak of war, the situation deteriorated significantly. Certainly, by March 1936 the situation was volatile enough that armed conflict was a real possibility.

Not including the Provisional Government which managed the transition after the fall of the Primo de Rivera dictatorship in 1931, the republic had 8 prime ministers (two of them who held the office more than once) and 15 governments by the time of the July 1936 coup attempt which signalled the start of the civil war. The longest-serving prime minister, Manuel Azaña, was in office for just over two years in total; the longest-serving government, the second Azaña ministry, lasted less than 18 months.

The extraordinary political polarisation which was the result of global economic depression and Azaña's rapid and far-reaching social reform programme in 1931-33, along with the fundamental weakness and instability of the republic's government, gave fuel to radical and revolutionary movements on both sides of the political spectrum.

Particularly important is the massive growth in the Spanish labour movement, which became a powerfully assertive political force in the republic. The socialist trade union, the Unión General de Trabajadores (UGT), had between one and two million members by the mid-1930s; the anarchist union, the Confederación Nacional del Trabajo (CNT), had an estimated two million members.

The Asturias miners' rising of 1934 provides a bloody illustration of how deeply divided Spanish politics had become. The entry of three right-wing ministers into Alejandro Larroux's government prompted a general strike — and, in the mining regions of Asturias, a full-scale uprising by the UGT, CNT and other factions on the radical left. The Asturian rising quickly evolved into an attempted revolution; workers seized mines and factories and occupied the provincial capital, Oviedo.

Larroux ordered the army, under the command of the generals Francisco Franco and Manuel Goded (both of whom would later become leading figures in the military rising that ignited the civil war) to crush the rising, which they did with extreme force — perhaps as many as 2,000 people were killed.

After Asturias, which demonstrated the capacity of the Spanish revolutionaries for large-scale armed insurrection, Spanish politics only polarised further. Throughout the first half of 1936, spontaneous violence was a common occurrence across Spain; assassinations, bombings, and running battles in the streets between left-wing workers and right-wing Falangists.

The pair of assassinations that are commonly seen as the final sparks that ignited the Spanish powder keg — the murder of the Guardia de Asalto officer José Castillo by Falangists on 12 July, and the killing in reprisal of conservative politician José Calvo Sotelo by Castillo's comrades the following day — were really only used as public pretext for the military stepping in to 'restore order'.

Right-wing elements within the military began plotting a coup d'etat as soon as the left-wing Popular Front alliance won the February 1936 election (though, in fact, you can reasonably observe that at almost any moment in the republic's history, there was at least one military coup being plotted somewhere within the armed forces.) That the military would attempt a coup would have come as a surprise to no-one — after all, there had been one attempted pronunciamiento against the republic already, when General José Sanjurjo attempted to seize control in August 1932.

What's more surprising than the military coup itself is the manner in which it failed; the immediate and large-scale intervention of revolutionary militias in defence of the republic, and the collaboration (however uneasy) between revolutionaries and republicans in the early days of the civil war was unlike anything seen before.

It's unlikely anyone could have predicted that the civil war would escalate to the level it did — certain key events, like the social revolution in Catalonia and the rise of the Spanish communists in the Madrid government were purely opportunistic, but had a material impact on the course of the war. But even if the consequences of the war were unforeseeable, the roots of conflict had been planted long before. To many Spaniards, it would perhaps have been more surprising if the republic hadn't come under attack.