The advantages of the civil war were that slavery was abolished and the union was restored. The disadvantages were that more American soldiers died than in any other war, and the economy of the South was destroyed.
The issue of slavery had been contested in the United States since the nation was formed. One of the major positives of the civil war is that Abraham Lincoln made the Emancipation Proclamation which abolished slavery, including in states in the south. Slavery became illegal in the United States overnight as a result and thousands upon thousands of slaves became free. The civil war also reunited the United States, restoring the union.
The biggest negative effect of the war was the death toll. Estimates vary, but according to the Civil War Trust, approximately 620,000 people died in the war. At the time this was about two percent of the total population of the United States. More Americans died in the civil war than in World War II, where 405,000 were killed. Many people died of wound infections due to bad medical conditions. The second-largest negative effect was the devastation of the southern economy, which had largely relied on slaves for all planting and menial work. The South's economy had to be completely transformed after the war.