Answer:
A is true. Slavery was one cause of conflict between the North and the South. The controversy between the Northern and Southern states over slavery was a major factor in the American Civil War.
B is false. The Emancipation Proclamation was signed by President Abraham Lincoln and declared all slaves free in the Confederate states of the United States. This freed the slaves, but did not end the dispute over slavery.
C is false. Slavery had been a controversial issue in the United States since the beginning.
D is false. Many people in the Southern states wanted to keep slavery legal.