The document discusses the construction of the first transcontinental railroad in the United States in the 1860s. It summarizes the various proposals over the decades to build such a railroad, the debate over potential routes, the Pacific Railroad Acts that incentivized and funded the construction by the Union Pacific and Central Pacific railroads, the main immigrant worker groups of Irish and Chinese who built it, and the impacts on trade, travel, Native Americans, and the connectedness of the country. Completion in 1869 united the eastern and western United States by rail and transformed the nation.