As Joan Robinson pointed out, following the opening of free trade with England, Portugal endured centuries of economic underdevelopment: "the imposition of free trade on Portugal killed off a promising textile industry and left her with a slow-growing export market for wine, while for England, exports of cotton cloth led to accumulation, mechanisation and the whole spiralling growth of the industrial revolution". Robinson argued that Ricardo's example required that economies be in static equilibrium positions with full employment and that there could not be a trade deficit or a trade surplus. These conditions, she wrote, were not relevant to the real world. She also argued that Ricardo's math did not take into account that some countries may be at different levels of development and that this raised the prospect of 'unequal exchange' which might hamper a country's development, as we saw in the case of Portugal.