There are a number of factors that allowed the United States to become industrialized in the years after the Civil War. Let us look at three of them.
First, there was the development of the railroads that opened the West to massive amounts of white settlement. The railroads were important for industrialization in at least two ways. First, the nation needed to industrialize just to build the railroads and the trains to run on them. This demanded huge amounts of steel which had to be produced industrially. Second, the creation of all the railroads allowed for a huge common market to be created. Raw materials could be moved easily to faraway factories where they would be made into usable goods. These goods could be shipped easily by train around the country. This made it possible for the US to industrialize on a large scale.
Second, there was the development of new technologies. One of the most important of these was the Bessemer Process for making steel. Since this process allowed steel to be made more quickly and cheaply, it increased the quantity of steel that was demanded by industries. This led the steel industry to get even bigger. Later, communications breakthroughs like the telephone and the telegraph allowed for instant communications between faraway places, thus making it easier to do business across long distances. Other inventions, such as the refrigerated train car and various office machines contributed to this process.
Finally, there was a massive influx of immigrants to the United States during this time. These immigrants were very important because they provided a huge pool of cheap labor. Because there was so much cheap labor available, industrial companies were able to hire the workers they needed to man their factories while still keeping costs low.
These three factors did more than any others to promote the development of industrialization in the US.