During the late 1800s, major improvements to a nationwide system of trade were made with?

During the late 1800s, major improvements to a nationwide system of trade were made with the development of strong transcontinental railroads.

Explanation:

During the late 1800s, business magnates and industrialist entrepreneurs such as Andrew Carnegie and Cornelius Vanderbilt enabled the American society to increase their wealth by leading the growing industries such as steel and constructing major railroad networks. Vanderbilt helped make railroad transportation more efficient by using new technologies and business organization, and the steel production enabled the construction of stronger railroads. Vanderbilt greatly improved the nation's transportation infraestructure and this allowed a more efficient transport of goods across the US. Therefore, goods produced in the west could reach the eastern states rapidly and, in consequence, be sold by trading with other nations.  

increasing defense spending.

explanation:

the answer is d trust me