126 SOCIAL SCIENTIST theories of unequal exchange for these too do not incorporate the fact of unequal productive capacities, monopoly and unilateral transfers but simply blow up the advanced country value-price model of competitive capitalism to a world scale. Marxists have not in fact developed a comprehensive theory of what we would call "really open economies", which incorporates the factors we have mentioned. One of the main reason has been the continuing intellectual strait jacket imposed by Ricardian trade theory on Marxists, no less than on mainstream theorists, combined with a misconceived adherence to the idea that competition of symmetrically placed capitals can capture the essence of imperialism . As the analysis of the exploitation of workers under capitalism was necessary, so too is the analysis of the mechanisms of neo-imperialism necessary today for the continuation of the revolutionary project initiated by Marx and Engels long years ago.