Spain in Revolt is a strange film. Its essentially an anti-franco film made during the Spanish Civil War. It has an English voice over, its incomplete, I've managed to find two of its (presumably) 3 reels intact and have combined them. Making what as far as I know is the most substantial collection of footage within it. The film's first reel is still missing, which is frustrating as in those days most films frontloaded their credits and production information, many of the question surrounding the film could be answered if just a part of that first reel were found.
I assume it was filmed in 1938 as the voice over has a present tense tone and speaks as if the events were happening as he was talking, and the footage I can identify comes from that year at the latest. The footage is a mix of scenes from the war, the Francoists are referred to as the rebels which probably confused some modern viewers, but the nationalist and fascist coalition was born out of an army mutiny in 1936, so loyalist Spain were the forces of the Republic which depending on who is doing the telling may or may not include the more radical elements like the Anarchist CNT/FAI militias, and the rebels were the Carlists, Falange party and Aristocratic officer corps.
Parts of the film are battle footage set to music, mostly classical and at times weirdly cheery. It includes some rare footage of fighting in Burgos which must've come from the first days of the war as it quickly fell to Franco who made that city his base of operations, and the aftermath of bombardments. It ends very confusingly on footage of the Pope and an appeal for peace. So I can speculate that whoever made this film was either an American liberal catholic whose sympathies were with the Spanish Republic, or were secular and didn't know anything about Catholicism but thought the Pope was a good stand in for peace and good will. I'm leaning in this direction because Catholicism in Spain and in the Vatican openly supported Franco, they supported him morally, economically and through the Carlist militia and over bands militarily. So, either this is a liberal Catholic trying to overcome the tension within themselves or it was made by someone who knew nothing about the politics of the Holy See.