The Spanish Protestantism as we see it now originates from the second half of the 19th century.

We'll show very briefly here what preceded it and what follows.

In the beginning of the 18th century the monarchy in Spain went over from the Austrians to the house of Bourbon, after the Spanish war of succession, 1702-1713. Those Bourbons were a reactionary and conservative family. 
Now in France we had the so called Age of Reason, and ideas from that source filtered slowly through to Spain as well, so that beginning 19th century Spain was ready for a liberal constitution.

In the meantime Napoleon Bonaparte had come to power in France, and he conquered Spain in his stride, but was unable to keep it. So after he was defeated Spain looked for a new king, one that could give them a real constitution,  and deemed Ferdinand VII fit for the role. So a constitution was written and proclaimed in 1812, in Cadiz, while it was sworn to in the nearby San Fernando, which claims as much honor in this matter as Cadiz itself. This first constitution has the popular name La Pepa, because it became law on the day of Saint John. (In Spanish shortened to Pepe.) 
Alas! To have a constitution did not mean to see it implemented! 

The 19th century proofed itself to be very unruly in Spain. Rivaling groups in society tried to take the power from each other time and again. Liberals and Conservatives knew different paths within themselves, besides there were the Carlists and the Republicans, all of them wouldn't give each other the time of day. 
That way the notion of liberty of religion got a variety of content in the course of time, from: there is freedom of conscience and religion for every Spanish subject, (very rare) to: Every Spaniard is per definition Roman Catholic, and strangers are by Gods Grace allowed to pursue their religion, but never in public. 

Now Ferdinand VII turned out to be an arch-conservative, and liberalism found to way to settle itself in Spain until the latter quart of the 19th century.
Ferdinand's daughter, Isabel II, was in some respects a conservative as well, under the influence of her ministers of state, who happened, one after the other, to be her lovers as well. As to matters of love life the Spanish society proofed to be more conservative than the queen and sent her packing in 1868. The generals Prim and Serrano, that initiated the coup, were liberals at heart, but wanted a monarchy for Spain, be it under conditions. Prim is said to have said: 'To find a democratic king in Europe is as hard as to find an atheist in Heaven!'

So the crown was offered to Amadeus of Savoy, who left the job after a year, it did not suit him nor was he suited for the job, and since he wanted no bloodshed on his behalf, he quitted, setting a beautiful example for history. In 1872 Don Carlos tried in vain his hand by starting the second Carlist war, and in 1873 the First Republic was proclaimed. 
This meant for Spain for the very first time since the inquisition: freedom of religion. The inquisition by the way was abolished by Ferdinand VII!

In 1874 the Bourbons returned to the throne with Alfonso XII, a son of Isabel, which meant an end to freedom of religion, and return of state religion. The RC variety of course. Which meant that there was freedom of conscience, but no possibility to share ones believes. Who thought different was persecuted.

Next comes Alfonso XIII in 1886, a nonentity of a king. Under his so called reign existed the dictatorship of José Antonio Primo de Rivera, from 1923-1930. In 1931 the king is extradited through some kind of left revolution. The king wished no civil war for his sake, and abdicated in good harmony before retiring to England.

Alfonso XIII had a deaf-mute son called Jaime, the father of Juan Carlos, who is now king. Jaime was Count of Barcelona. 

The second Republic was proclaimed in 1931, but ended in a terrible struggle for power. In the mean time the state-religion was abolished again, and so a new period of religious freedom started, though it lasted only until 1936. Since this republic originated from the left, and of course the Protestants liked the freedom of religion, later they were reproached with being of course leftwing. And so they are against their country, that is why they have been persecuted sorely under Franco. But the odium of not being good Spaniards has pursued them - until today. 

In 1936 it seemed obvious that the Communists were about to seize power (La Pasionaria) and then the uprising started in Morocco under general Franco. This insurrection was pointed against the republican government, which had hardly any power. Now the Communists were determined to seize the power. 
And so the Civil War started in 1936 and lasted till 1939. Franco won the war. He restored the position of the RC church and the monarchy, but without a king. Jaime was deemed unfit, and his son Juan Carlos was being trained for the kingdom to come. Franco was head of state, with the title of Caudillo, which means commander-in-chief. Only at the end of his life he brought Juan Carlos to the fore. It is obvious that Protestants have no link with him at all, since he came from Franco's stable. 

Whenever Franco had captured a part of Spain, the Protestant Churches and schools were closed, the ministers murdered, chased, exiled, silenced... 

In 1939 the civil war was ended. Hemmingway was one of the many combatants from abroad.

As mentioned many a Protestant was socialist, because the socialists were in favor of abolition of official religion. So they were regarded as enemies of the state afterwards. (In the South there existed a 'red' clergy, that saw the misery of the people, the deep poverty, whilst the top brass lived the good life in Madrid.) (Somebody told us that trade union literature was printed in the South under the care of the red priests. They have been persecuted during the Republic, by the way.)

What added to the negative feelings untoward the Protestants was the fact that the English and Americans the Protestant churches used for espionage. Ever since England owed Gibraltar, there have been Anglican churches. They were one of the main sources for the propagation of the Protestantism in Spain, so the Protestant churches in Spain were rather closely linked to Gibraltar, which was for them a gate to freedom.

The grief of the civil war is still lurking in the backs of the Protestant minds. One of the sores is that the monument for the fallen, which Franco had built in the Valle de los Caídos, not far from Madrid, was only remembering Franco's dead. (It has been built by prisoners, by the way, of which very many died!) The monument could and should have been a beginning of conciliation, in the Protestant view, and they blame the R.C.C. as well for their lack of zeal to fulfill their calling to the way of the gospel in that respect.

Spain kept itself out of the World War II, because Franco had good relations with Germany, and he managed to keep his country neutral. But not that neutral: many a refugee that tried to pass through Spain to England was interned. Franco did weaken the position of the Allied Forces by keeping himself out of the war.