To this conception of Ricardo's, Sismondi's _Nouveaux Principes_ were a powerful challenge, and the dispute as a whole turned also on this point. Ricardo could not deny the fact of crises which had but recently passed over England and other countries. What was at issue was the explanation for them. Right at the outset of their debate, Sismondi and Ricardo had agreed on a remarkably lucid and precise formulation of the problem, excluding the question of foreign commerce altogether. Sismondi grasped the significance and necessity of foreign trade for capitalist production, its need for expansion, well enough; in this line he was quite in step with Ricardo's Free Traders, whom he considerably excelled in his dialectical conception of the expansionist needs of capital. He fully admitted that industry 'is increasingly led to look for its vents on foreign markets where it is threatened by greater revolutions'.[200] He forecast, as we have seen, the rise of a dangerous competition for European industry in the overseas countries. This was after all a creditable achievement in the year 1820, and one which reveals Sismondi's deep insight into the relations of capitalist world economy. But even so, Sismondi was in fact far from conceiving the problem of realising the surplus value, the problem of accumulation, to depend on foreign commerce as its only means of salvation, a view attributed to him by later critics. On the contrary, Sismondi was quite explicit in the sixth chapter of volume i:[201] 'In order to make these calculations with greater certainty and to simplify these questions, we have hitherto made complete abstraction from foreign trade and supposed an isolated nation; this isolated nation is human society itself, and what is true for a nation without foreign commerce, is equally true for mankind.' In other words: in considering the entire world market as one society producing exclusively by capitalist methods, Sismondi grounds his problem in the same premises as Marx was to do after him. That was also the basis on which he came to terms with Ricardo. 'From the question that troubled us, we had each of us dismissed the instance of a nation that sold more abroad than it needed to buy there, that could command a growing external market for its growing internal production. In any case, it is not for us to decide whether fortunes of war or politics could perhaps bring forth new consumers for a nation--what is needed is proof that a nation can create these for itself simply by increasing its production.'[202] This is how Sismondi formulated the problem of realising the surplus value in all precision, just as it confronts us throughout the ensuing era in economics, in contrast with Ricardo who actually maintains along with Say, as we are already aware and shall show in further detail, that production creates its own demand.