Final answer:
The westward expansion and the California gold rush had a profound impact on the stability of the nation.
Step-by-step explanation:
The westward expansion of the 1840s and 1850s, along with the California gold rush, had a significant impact on the stability of the nation as a whole. The population of the United States grew rapidly during this period, leading to increased land-hunger and the desire for economic opportunities in the west. This expansion also influenced U.S. foreign policy and played a role in the tensions with Mexico. The discovery of gold in California further accelerated westward migration and contributed to the sectional divide.