In his notes on the history of economic thought in 1861-63, first published as Theories of Surplus Value (but in fact the second draft of Capital, volume 1), Marx comments on the way a rich country can exploit a poorer one.
He argued: “Say, in his notes to Ricardo’s book translated by Constancio, makes only one correct remark about foreign trade. Profit can also be made by cheating, one person gaining what the other loses. Loss and gain within a single country cancel each other out. But not so with trade between different countries. And even according to Ricardo’s theory, three days of labour of one country can be exchanged against one of another country—a point not noted by Say. Here the law of value undergoes essential modification. The relationship between labour days of different countries may be similar to that existing between skilled, complex labour and unskilled, simple labour within a country. In this case, the richer country exploits the poorer one, even where the latter gains by the exchange, as John Stuart Mill explains in his Some Unsettled Questions.” (MECW 32 p.294)
Marx also believed that foreign trade was vital for the process of transforming concrete labour into abstract labour. Marx wrote: “But it is only foreign trade, the development of the market to a world market, which causes money to develop into world money and abstract labour into social labour. Abstract wealth, value, money, hence abstract labour, develop in the measure that concrete labour becomes a totality of different modes of labour embracing the world market. Capitalist production rests on the value or the transformation of the labour embodied in the product into social labour. But this is only [possible] on the basis of foreign trade and of the world market. This is at once the pre-condition and the result of capitalist production.” (MECW 32 p.388)
Marx developed some of these insights in Capital volume III, written in 1865 but only published by Engels in 1894. Marx argued: “Since foreign trade partly cheapens the elements of constant capital, and partly the necessities of life for which the variable capital is exchanged, it tends to raise the rate of profit by increasing the rate of surplus-value and lowering the value of constant capital. It generally acts in this direction by permitting an expansion of the scale of production. It thereby hastens the process of accumulation, on the one hand, but causes the variable capital to shrink in relation to the constant capital, on the other, and thus hastens a fall in the rate of profit. In the same way, the expansion of foreign trade, although the basis of the capitalist mode of production in its infancy, has become its own product, however, with the further progress of the capitalist mode of production, through the innate necessity of this mode of production, its need for an ever-expanding market. Here we see once more the dual nature of this effect. Ricardo has entirely overlooked this side of foreign trade.”
“Another question — really beyond the scope of our analysis because of its special nature — is this: Is the general rate of profit raised by the higher rate of profit produced by capital invested in foreign, and particularly colonial, trade?
“Capitals invested in foreign trade can yield a higher rate of profit, because, in the first place, there is competition with commodities produced in other countries with inferior production facilities, so that the more advanced country sells its goods above their value even though cheaper than the competing countries. In so far as the labour of the more advanced country is here realised as labour of a higher specific weight, the rate of profit rises, because labour which has not been paid as being of a higher quality is sold as such. The same may obtain in relation to the country, to which commodities are exported and to that from which commodities are imported; namely, the latter may offer more materialised labour in kind than it receives, and yet thereby receive commodities cheaper than it could produce them. Just as a manufacturer who employs a new invention before it becomes generally used, undersells his competitors and yet sells his commodity above its individual value, that is, realises the specifically higher productiveness of the labour he employs as surplus-labour. He thus secures a surplus-profit.
“As concerns capitals invested in colonies, etc., on the other hand, they may yield higher rates of profit for the simple reason that the rate of profit is higher there due to backward development, and likewise the exploitation of labour, because of the use of slaves, coolies, etc.
“Why should not these higher rates of profit, realised by capitals invested in certain lines and sent home by them, enter into the equalisation of the general rate of profit and thus tend, pro tanto, to raise it, unless it is the monopolies that stand in the way. There is so much less reason for it, since these spheres of investment of capital are subject to the laws of free competition. What Ricardo fancies is mainly this: with the higher prices realised abroad commodities are bought there in return and sent home. These commodities are thus sold on the home market, which fact can at best be but a temporary extra disadvantage of these favoured spheres of production over others. This illusion falls away as soon as it is divested of its money-form. The favoured country recovers more labour in exchange for less labour, although this difference, this excess is pocketed, as in any exchange between labour and capital, by a certain class. Since the rate of profit is higher, therefore, because it is generally higher in a colonial country, it may, provided natural conditions are favourable, go hand in hand with low commodity-prices. A levelling takes place but not a levelling to the old level, as Ricardo feels.
“This same foreign trade develops the capitalist mode of production in the home country, which implies the decrease of variable capital in relation to constant, and, on the other hand, causes over-production in respect to foreign markets, so that in the long run it again has an opposite effect.” (MECW 37 pp.235-237)