Answer:
To slow down the arms race.
Explanation:
The answer is D. Farming settlements in the Indus Valley River began being established in 4000 BCE.
After the civil war there was a huge surge to rebuild the infrastructure of the U.S. many Americans wanted to move west to escape the horrors of the civil war, which started the race to the west coast (intercontinental railroad)
Sickness was a big thing brought from there as we were not used to there sicknesses and we were not used to there's it's a lot like the Aztecs and the Spanish the Spanish brought small pocks
