Answer:
New business practices, new technology, and the expansion of railroads
Step-by-step explanation:
The Gilded Age was a time in America during the late 1800's and early 1900's that focused saw a rapidly growing economy based around industrialization. The development of new business practices helped to create this new economy. This included vertical integration and horizontal integration. Both of these business structures helped to create monopolies, like the one that John D. Rockefeller had in the oil industry.
New technology like the creation of the assembly line, the bessemer process, etc. helped to spark growth in different markets. Lastly, the increase in railroad mileage allowed for the connection of the entire continental US, making the shipping of goods and materials easier.