So, from the way the question is posed, it seems like you may be inadvertently violating the subreddit's 'Homework' rule - that is, we aren't going to do your work for you, but can suggest resources if you ask. I’ll answer it assuming your intent was not to break any rules, but the mods may step in and ask you to rephrase it.

In any case, I find the premise of the question itself to be a bit awkward - 'valid' is a very loaded term (are political or ideological grounds never valid? would opposing Hitler require a socio-economic analysis to be worthwhile?). Even if a less loaded term was used to frame the question, I think it’s problematic to assume that there is a neat line between material, objective concerns and political motives. For instance, where is the line for a middle-class business owner who is afraid that the Popular Front’s proposed policies are going to drive him out of business? The concern may be material, but the apprehension is political.

There is a very broad literature on the causes of the war, from a variety of perspectives. You’ll find discussion of the motives of the rebels and their supporters in most text dealing with the Spanish Civil War, but quite a few accounts deal specifically with the pre-civil war period, such as:

Gabriel Jackson, The Spanish Republic and the Civil War, 1931–1939 (Princeton, 1965); Fernando del Rey Reguillo, The Spanish Second Republic Revisited: From Democratic Hopes to Civil War (1931– 1936) (Brighton, 2012); Stanley Payne*, The collapse of the Spanish Republic, 1933–1936 (New Haven, 2006); Paul Preston, The Coming of the Spanish Civil War: Reform, Reaction and Revolution 1931–*1936 (London, 1994).

This selection alone should give you a pretty good variety of arguments and perspectives, but there are many more out there. Good luck!