The Union Pacific was chartered by Congress, through the Pacific Railroad Act of 1862, to construct a portion of the first transcontinental line, starting in Omaha and proceeding westward through the Platte River Valley. Construction crews comprised the brawn of Irish immigrants and large numbers of war veterans, who pushed the lines across Nebraska, southern Wyoming and into northern Utah, while encountering hostile American Indians. Feeling it imperative to protect their families and homeland, those Indians repeatedly attacked without warning, while the Union Pacific was left to act as its own army.
After four years of labor, this leg of the transcontinental line linked with the Central Pacific Railroad at Promontory Point, Utah on May 10, 1869 with the now-famous golden spike. It was now possible to leave San Francisco and arrive in New York in 10 days. Misuse of public monies was rampant in this venture, particularly the fraudulent activities of Crédit Mobilier. The public was charged $94 million for costs totaling only $44 million.
The Union Pacific was forced into receivership during the depression of the 1890s, but was brought back to prominence by E.H. Harriman.