Between 1500 and 1750 most economists advocated Mercantilism which promoted the idea of international trade for the purpose of earning bullion by running a trade surplus with other countries. Ricardo challenged the idea that the purpose of trade was merely to accumulate gold or silver. With "comparative advantage" Ricardo argued in favour of industry specialisation and free trade. He suggested that industry specialization combined with free international trade always produces positive results. This theory expanded on the concept of absolute advantage.