Final answer:
W.H. Auden participated in the Spanish Civil War due to ideological opposition to the rise of fascism in Europe, and a sense of moral duty to support the Republican cause against the Nationalist forces led by Francisco Franco.
Step-by-step explanation:
German poet W.H. Auden participated in the Spanish Civil War like many other intellectuals and artists of the time, because of the ideological battle it represented against the rising tide of fascism in Europe. Auden, like others, was deeply concerned with the political developments of the 1930s, as fascist regimes took power in countries like Italy and Germany, and the potential spread of fascism to Spain was met with alarm by those who supported democratic, socialist, or communist ideologies. Auden's participation was driven by a sense of moral duty to support the Republican cause against General Francisco Franco and his Nationalist forces, which were backed by Hitler’s Nazi Germany and Mussolini's Italy. This conflict was characterized by brutal violence and was a precursory fight to the broader struggle against fascism that would engulf Europe during World War II.