Answer:
Although unified politically, the United States was hurt by sectionalism, or competition among sections or regions of the country. In the early 1800s three major sections emerged: the industrial Northeast, the agricultural South, and the largely frontier West.
Explanation:
The correct answer is disease.
Many of the Europeans were carrying disease that they had acquired immunity to since the diseases had been rampaging around Europe for centuries.
But the people of the Americas did not have the immunity and it almost wiped them out.