IIRC, Marx thought that communism would only be successful in an industrialized society, working on finding confirmation on that.
This is what I get for not reading up, Marxism is about:
The productive capacity of society is the foundation of society, and as this capacity increases over time the social relations of production, class relations, evolve through this struggle of the classes and pass through definite stages (primitive communism, slavery, feudalism, capitalism). The legal, political, ideological and other aspects (ex. art) of society are derived from these production relations as is the consciousness of the individuals of which the society is composed.
So in pure philosophical terms, the productive capacity is broadly defined. You might find scholars and philosophers who would define it more narrowly, but I don't think you can exclude argiculture from the "productive" definition. It certainly is not excluded in communist nations.
Source is wiki, fyi. I read the Communist Manifesto once, probably 20 years ago. Never wanted or needed to go back and re-read it. I probably should, if nothing else than to demonstrate why I am not even close to a communist, regardless of what Glenn and Rush may claim.
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Project Gutenburg has it, but they seem to be having website issues. I don;t recall it being a particularly long book. Wiki has some excerpts though:
Freeman and slave, patrician and plebeian, lord and serf, guild-master and journeyman, in a word, oppressor and oppressed, stood in constant opposition to one another, carried on an uninterrupted, now hidden, now open fight, a fight that each time ended, either in a revolutionary re-constitution of society at large, or in the common ruin of the contending classes.
And specifically one of the 10 tenets of traditional communism:
Combination of agriculture with manufacturing industries; gradual abolition of the distinction between town and country, by a more equitable distribution of the population over the country
and:
Equal liability of all to labour. Establishment of industrial armies, especially for agriculture.
I see that as a merging of ag and industry in the minds of the communist. According to my reading of that, they are the same, they share the same struggles, and are all generally considered proletariat.
http://en.wikipedia.org/wiki/The_Communist_Manifesto