The expansion of the railroads had almost diametrically opposite effects on Native Americans and white settlers.
White settlers generally benefitted from the railroads. The railroads allowed them to settle more places since they could be connected to markets in more populated areas. The railroads brought them goods that they needed and transported the things they produced. This allowed white settlement to expand dramatically.
Of course, the white settlement came at the expense of the Native Americans. The penetration of the railroads into their land progressively forced them off more and more territory. The coming of the railroads meant that huge streams of white people and their technology could overwhelm the Native Americans. This led to the situation where all the Native American tribes were conquered and pushed on to reservations.
Thus, the railroads impacted these two groups in very different ways.
The expanding railroads across the old American west provided a direct route for many white settlers to access land that previously would have been difficult to reach. This land was distributed to many of the white settlers through the Homestead Act. However, the reverse is true for Native Americans. Various tribes were forced to relocate to reservations, which were usually composed of the poorest quality of land. The railroads also disrupted the migration patters of the buffalo and helpled lead to its ultimate demise. The downfall of the plains indians resulted from this action.