Frontier: Refers to a geographical area at or beyond the edge of settled territory. The American frontier moved steadily westward throughout history.
Transcontinental Railroad: A railroad line completed in 1869 that connected the East Coast with the West Coast, facilitating transportation and settlement across vast distances.
Pioneer: A person who is among the first settlers or explorers of a new area or region. Pioneers played a significant role in expanding westward during American history.