That was the easy part: fear. They know very well the character of the Spanish people (they ruled Spain during 14 years) and they control the mass media.
And not fear to terrorists, but “economic” fear. During the morning of 3/11 the police kept saying it was ETA. Some said that if that was confirmed, article 155 of the Spanish Constitution should be applied to the Basque region, abolishing the autonomy there. That was an economic threat not only for the Basque region, but also for Catalonia, because without autonomy they wouldn’t have the privileges they enjoy now above the rest of Spaniards.
Even if article 155 was not applied, the truth is that any regional nationalist movement would be over in Spain if ETA was found the perpetrator.
That is, there were overwhelming economic interests, at top level but also for regular citizens from the nationalist regions.
The coup did not affect severely the right wing Popular Party, which only lost 300,000 or 400,000 votes out of ten million, but mobilized people ideologically far away from it who in these elections, initially, thet did not want to vote.
In the end, the Socialist party got one million votes above what the polls showed before the attack (out of a total of 23 million), which, I suspect, was not enough for what the mastermind intended: the discredit of the Popular Party and any right wing policy forever.
Very interesting. Thank you for the info.