Final answer:
The major era described in the question is the Industrial Revolution in the late nineteenth century, characterized by the rise of big business, increased unionization of workers, extended railroad building, and expanded industrial growth.
Step-by-step explanation:
The major era described in the question is the Industrial Revolution in the late nineteenth century.
During this period, there was a rise of big business, such as Andrew Carnegie's steel empire, and increased unionization of workers as they fought for better working conditions and fair wages. Additionally, there was extensive building of railroads, which connected different parts of the country and facilitated the expansion of industrial growth.