From a wonderful interview of Eric Siblin, the author of a book on cellist Pablo Casals popularization of Bach's cello suites, by Scott Horton of Harpers:
When the ideological barricades went up in Europe in the 1930s Casals, like many, took sides. His position was not surprising given his background. As someone whose father had been an anti-monarchist Republican, and as a native Catalan—which meant being very wary of Madrid’s centralizing powers—Casals was predisposed to favor the Republican side in the Spanish Civil War. When Franco and his fascist troops, assisted by Hitler and Mussolini, won the civil war in early 1939, Casals was forced into grief-stricken exile. He remained an anti-Franco activist for the rest of his life, enlisting his reputation and cello for the cause. The most famous instrumentalist of his day, Casals went so far as to silence his cello, refusing to perform in any country that had diplomatic relations with the Franco regime in Spain. Casals would have related to the politics of Bono more than Bach.
His pioneering recording of the cello suites was made towards the end of the 1930s when the Spanish Civil War was convulsing his homeland. That monumental recording, which has never gone out of print, has remained the touchstone for every cellist since. Had the civil war not been raging in Spain, I doubt there would have been the same degree of urgency, desperation, and hopefulness in that epic recording.