In the second half of the 1800s the federal government encouraged the building of transcontinental railroad by

Because the Railroad companies that built the railroads were able to keep the land that the railroads passed though, so the Government gave the Companies land grants to give them incentive to build and fund the Railroads,
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Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.