How was the US economy transformed in the Industrial Revolution of the late 19th century?

Of course, the most important way in which the economy was
transformed was in the fact that it became more industrial.  This meant that more and
more things were mass produced in factories instead of being made by hand in shops. 
This was a major change.

Along with this came at least two
other changes.

First, the US economy became much more
nationalized.  In other words, the whole country became one big market instead of being
split up into a lot of little regional markets.  This happened because of the huge boom
in railroad construction.  The railroads made it possible for goods to be shipped around
the country quite easily.  Therefore, people in all parts of the country could sell to
one another.

Second, the economy came to be dominated by
large companies.  As industrialization continued, the "robber barons" created huge
companies that killed off competitors.  This was a huge change from an economy that was
dominated by small firms run by individuals.