Answer:
The expansion of the United States in the 19th century, through policies such as Manifest Destiny and the annexation of territories, had negative consequences for the country both militarily and economically. The acquisition of new territories, such as the Mexican-American War, resulted in military conflicts and the displacement of indigenous populations. Additionally, the expansion led to economic issues, as the country struggled to integrate and govern the new territories, particularly in the case of slavery in the newly acquired territories which ultimately led to the civil war.