b) Union Pacific Railroad and Central Pacific Railroad

The Union Pacific Railroad and Central Pacific Railroad were the two companies that connected to form the first transcontinental railroad in the United States in 1869. The Union Pacific built from the east, starting in Omaha, Nebraska, while the Central Pacific built from the west, starting in Sacramento, California. Their junction at Promontory Summit, Utah, symbolized the unification of the nation by rail. This monumental engineering feat facilitated westward expansion, transformed American transportation, and had a profound impact on the country’s economy and settlement patterns. The transcontinental railroad represented a major achievement in infrastructure and engineering, significantly altering the course of American history.