1869
In 1865, America was unified through war. Four years later in 1869, the country was unified by steel. On Nov. 24, Central Pacific railroad workers pushing east from California met up with Union Pacific workers pushing west from Omaha, Nebraska. The transcontinental railroad was completed when the two parties met in Promontory, Utah. The moment signaled the passing of the American frontier, with its caravans of wagon trains carrying pioneers on long, dangerous journeys west.