You must remember at the time of his writing agriculture was seen as the main way nations traded with each other, what Ricardo suggested was ground breaking. In his writings we see the development of the gold standard for international monetary policy. This was in use up until the 1970 s. There may be a point in time when the workers revolt against farmers and landowners. Technology was seen to be both a blessing to generate increased profits whilst at the same time a menace to generating unemployment.
Free trade is essential.
Out of free trade is born the concept of comparative advantage, which in turn should be used to eradicate unemployment. The use of gold as an international trading standard. Reduced taxation leads to economic growth.