Answer:
D. to prevent the spread of communism to South Vietnam
In general, this movement had a negative impact since lots of the expansion involved moving into territories that were controlled by European nations. Although most of the time physical conflict was avoided.
The British. Because they promised them that they would limit the colonist westward migration. (Which they did not follow through with)
Majority of Southerners were opposed to Lincoln’s stance on slavery.
They saw him as a threat to their livelihood and harbinger of secession.