<em>Slavery in the Americas was based on race.</em>
The Civil War in the United States started by the many differences the Northern states had with the confederated states, basically on slavery. The North supported desegregation meanwhile the South supported slavery. Indeed, slavery was an important part of the Southern economy.
On April 12, 1861, the Confederated Army attacked Fort Sumter, in Charleston, South Carolina. This incident initiated the Civil War. One advantage for the North at the start of the Civil War was the North had a larger population.
The correct answer should be the third one you listed. The "current drag" then is a device that is used in order to measure the sub-surface currents. This device and the measurements it provides are extremely important for the field of oceanography which studies the aspects of the oceans both the physical and the biological ones.
Brown v. Board of Education of Topeka was a landmark 1954 Supreme Court case in which the justices ruled unanimously that racial segregation of children in public schools was unconstitutional.
