How did railroads affect empire building in afro-eurasia between 1860 and 1918?

The expansion of the railroads in the late 1800s was instrumental in helping the US economy boom.   It did this in two ways. 

First, the railroads created a tremendous amount of demand for goods and labor on their own.  As the railroads were being built, they needed huge numbers of people to build them. 

missouri compromise of 1820 which prohibited slavery