What geographic feature might have prevented the spread of christianity to other areas?

The answer to this would depend on the place and time period we are referring to. Christianity originated in the Middle East, and from here, it spread all over the world. At its origin, Christianity's spread could have been complicated by some geographic features, such as the deserts of the Middle East. As it spread, it could have encountered other barriers, such as oceans and mountain ranges.

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.