The answer is wheat. Wheat was one of the most exported products in the US because of its abundance. North America owns the largest fertile lands in the world. They make up 50 percent of the kernel production in the world. Wheat was being exported during the 19th century because most countries like Russia, Great Britain can not grow such product because of its climate and geographical location.
Following WWI in North America and most of Europe there was a recession that led to economic decline. The recession in the United States did not last long and was followed by nearly a decade of major economic growth that made the United States the most powerful economy in the world.
