Answer: Artificial intelligence, Biomedical techs, coal, the atomic bomb, and drones.
Brainliest please i need it bad
It is D) Slave trade in Washington I hope this helps :D
Answer: the decision by the United States government to prevent additional settlement
Explanation:
What was meant by the "closing" of the Western frontier was that the United States government wanted to prevent additional settlement.
This decision was as a result of the government's plan to promote the westward expansion after the Civil War, but however, they had to close the Western frontier to prevent additional settlers.
