It was on 17 July 1936 that Franco attempted a coup against the elected government of Spain, starting the Spanish Civil War.
In February, a Popular Front had assumed gov't composed of a coalition of liberal republicans, socialist workers (PSOE), left republicans, regional autonomists, and the Communist Party. The Communists held a tiny number of seats in parliament: 15 or 17 out of 470.
Franco, though, insisted that his nationalist military was saving the country from the control of "Marxists," "communists," and agents of a Bolshevik revolution. The government was constitutionally elected under Spain's existing democratic system, and was under the control of liberal republicans. Was Franco exaggerating? Franco being Franco? Or was he trying to justify his takeover?
He portrayed the coup as:
• saving Spain from atheism,
•preventing a Bolshevik revolution,
• defending Christianity,
•restoring law and order.
Spain in mid-1936 was experiencing severe political polarization.
But portraying the elected government as simply "communist" collapsed many different political movements into a single enemy and made the coup easier to justify to supporters.
Political scientists sometimes describe this as outgroup exaggeration or threat inflation. It serves several functions:
•mobilizing supporters,
•creating a clear moral contrast,
•justifying extraordinary measures,
•discouraging compromise by framing opponents as existential threats.
Several of us here on the forum, including Rick himself, iirc, recommend taking Nick Lloyd's walking tour of Barcelona for a real feeling about this period, and Lloyd has published a guide based on his many years of tour-leading,
Forgotten Places: Barcelona and the Spanish Civil War
A geographically/traveler - oriented book that is often mentioned is
The Battle for Spain: The Spanish Civil War 1936–1939 — by Antony Beevor
More hardcore history buffs will enjoy Paul Preston's The Spanish Civil War: Reaction, Revolution and Revenge.
For a more basic orientation to the period, check out Helen Graham's, The Spanish Civil War: A Very Short Introduction
Where have you gone that you learned more about the war while visiting the big cities of Madrid and Barcelona, or the key locations like Guernica and the Ebro battlefields?