Frontier: The term "frontier" refers to the unexplored or unsettled areas at the edge of a settled region. It represents the boundary between civilization and wilderness.
Manifest Destiny: Manifest Destiny was a belief held by many Americans in the 19th century that it was their God-given destiny to expand westward across North America, which led to rapid territorial acquisition.
Homesteading: Homesteading is a process through which individuals could acquire land from the government by settling on and cultivating it for a certain period. This played a significant role in westward expansion as settlers moved further into frontier areas.