The USA was known as the bread basket of the world during the 19th century.
The different factors responsible for the expansion of agriculture in the USA are
(i) The growth of urban population and export market encouraged farmers to produce more wheat.
(ii) A spread of railway made it easy to transport the grain.
(iii) Introduction of machines helped in production.
(iv) During the First World War Russian supplies of wheat were cut off and the USA had to feed Europe.