Final answer:
The rapid population growth in the West in the late 1800s was primarily caused by demographic, economic, and political pressures.
Step-by-step explanation:
The rapid population growth in the West in the late 1800s was primarily caused by demographic, economic, and political pressures. The population of the United States grew rapidly during this period due to factors such as increasing land hunger, declining soil fertility in the east, and fears of British occupation. Additionally, economic motivations, such as Eastern merchants wanting control of west coast ports for trade with Asia, also contributed to the rapid growth.