What is the primary reason that explains why the democrats and republicans have endured as the two major political parties?

The main reason that explains why the democrats and republicans have endured as the two main political parties the existence of single member election districts. This has led to a situation whereby the winner takes all given that each area is divided into a number of physically defined voting districts that are represented by a single person

other sources of text

explanation:

this can be magazines, news reports, scholarly articles, textbooks, research papers etc.

while it was true that the cotton gin reduced the labor of removing seeds, it did not reduce the need for slaves to grow and pick the cotton.

explanation:

before eli whitney's invention of the cotton gin, picking and cleaning cotton was a slow, labor-intensive job. workers, usually slaves, had to pick the seeds from the cotton fibers by hand. this invention made it possible to grow large amounts of cotton on big farms and make money.