Prove that in the second half of the 19th century, the rapid economic development of the United States begins.

In the second half of the 19th century, the rapid construction of railways began in the United States. This helped develop the domestic market. At the same time, the country had a lot of natural resources (coal, iron, oil). For work, it was possible to exploit slaves who came from other countries, this made it possible to save on labor. There was still not enough of it, and the proletarians could get land freely to work on it. This led to the need to improve the technique. New technologies began to appear. This led to the rapid development of production and economy.