The most active period of the Trans Atlantic slave trade was during the period between the years 1501 to 1867. The Atlantic slave trade or Trans Atlantic Slave Trade became very popular between the 15th and the 19th century. Most of the slaves were captured and taken to the New World. The transport of slave trade took place via the Triangular Trade route.
Reason they would support the Vietnam war is to support President Truman use of containment. Which was to limit the spread of communism throughout the world.
A reason not to go to war is the fear of being drafted which was common during the Vietnam War.