This document discusses the key factors involved in westward expansion in the United States during the 19th century. It describes the physical obstacles like mountains and rivers that settlers had to overcome in crossing the country. It also discusses the major role of the transcontinental railroad in facilitating faster and cheaper travel west, as well as how it impacted the environment. Additionally, it examines how immigrants from China, Europe and other places contributed to westward expansion through helping to build the railroad and settling on the Great Plains, despite facing discrimination. Finally, it analyzes the negative effects of expansion on native Americans, including being forced onto reservations and having their children educated in white schools.