So are you just asking why businesses got to be so big in the late 1800s? If so, the main reason is technology.
Before the civil War, especially, it was very difficult to make a really large business. There were not that many large machines that could produce goods on a large scale. Even if there had been, there were not any huge markets, tied together by railroads, that could consume all the goods. The lack of railroads also made it much harder for factories in one area to get raw materials from another area. It was much more necessary to have smaller factories spread around the country.
As the 1800s went along, the boom in railroad tied markets together much more efficiently. Along with this came technological improvements that made larger machines possible. In addition, things like the telegraph made communications between parts of a large company much more possible.
Because of all these technological changes, large scale enterprise became much more prevalent in the late 1800s.