Answer:
B.When leaders in Congress began to support the cause, pro-slavery supporters turned against the nation.
Step-by-step explanation:
Abraham Lincoln's has anti-slavery stand and when he won the election for the post of President of the United States in 1860, seven southern States secede from the Union by organizing the Confederate States of America. But Lincoln was again clear that any threat to Union was treated with grieve circumstances. And these situations stated the Civil War of The United States of America which divided the country for almost four years.