The election of Abraham Lincoln to the Presidency of the United States in 1860 triggered the succession of most of the southern states where slavery was legal, because the wealthy whites who dominated those states feared that the federal government would force them to give up slavery. The result was the four bloodiest years in all of American history. But what if cooler heads had prevailed and the Civil War had never happened? What if instead the South had remained in the Union?
For one thing, the fact that so many young men had not died in battle meant that the USA would have been able to conquer the western regions much faster than it actually did, and the Native American tribes living on those lands would have been even more brutalized in the process. Anti-immigrant sentiments would have been greater in the late 19th Century then they were, since there would be no perceived need for more people to come to the USA from other parts of the world. States that entered the Union after the Civil War might still have had slaves if they were in the southwest, but the Industrial Revolution of the late 19th Century would at the same time had made slavery largely unprofitable. Both northern abolitionists and European states opposed to slavery might have succeeded in putting enough pressure on the United States for it to pass a Constitutional Amendment abolishing slavery, but the southern states would have been able to block amendments granting citizenship and voting rights to freed blacks. As a result, the Supreme Court of the United States would have had no legal basis to condemn the Jim Crow laws and procedures of the South, resulting in racial segregation continuing to this very day. Many aspects of American culture, such as rock & roll and hip/hop music, would never have become popular among white youths. The United States would have regarded Mexico as an invader due to so many of its people coming undocumented across the border between them and this might have eventually led to another war with Mexico by the end of the 20th Century. The Cold War between the United States and the Soviet Union would have lasted much longer and been more damaging to the interests of the USA around the world because most other nations would see the Soviets are more enlightened and honorable than the racist Americans. Most black Americans would have been far more supportive of Communism and this in turn would have made capitalist supporting whites hate blacks even more.
.So the ultimate result would have been an America that was even MORE racist than today!