COMPARATIVE ADVANTAGE AND PROTECTION 181 
causes of comparative advantage stand others which are often 
quite as effective. It would be going too far to say that the 
physical causes are shown to be of secondary importance. But 
human causes — man’s ways of doing things — play so large a 
part and combine so constantly with the physical causes that it 
is often difficult to say which dominate. 
Agricultural products have always constituted the largest part 
of American exports. They still remain so, even tho non-agri- 
cultural products contribute a greater share than they did thru 
the nineteenth century. A new country, with abundance of fertile 
land, finds its labor most effective in the extractive industries. 
Hence the United States long was, and still is, a steady exporter of 
wheat, meat products, cotton. In the same way Canada is now a 
heavy exporter of wheat. Wheat is specially adapted to extensive 
culture, and is easily transportable; it is the commodity for which 
nature gives a clear comparative advantage to a new country in 
the temperate zone. The international trade of the United States 
was long determined chiefly by the country’s special advantages 
for the production of wheat and similar agricultural staples. 
But it is not merely the natural resources which have told, but 
the manner in which they were used. From the first, inventiveness 
and ingenuity were shown. The United States early became 
the great country of agricultural machinery. Especially during 
the second half of the nineteenth century, the skill of the makers 
of agricultural implements and the intelligence of the farmers who 
used the implements were factors not less important than the great 
stretches of new land. Still another factor of importance was 
the cheapening of transportation. From the very beginning, the 
Americans have been energetic and successful in overcoming the 
vast distances of the country. Our railroads have cheapened 
long hauls as nowhere else. The most striking advances in this 
combination of machine-aided agriculture with cheap transpor- 
tation were made in the last third of the nineteenth century. 
Then new lands were opened, and agricultural products exported, 
on a scale not before thought possible. It has already been 
pointed out that when the effectiveness of labor is spoken of, the