In addition, the federal government was controlled by the Southern pro-slavery majority until about 1850. They would have tried to use any strong federal power

In addition, the federal government was controlled by the Southern pro-slavery majority until about 1850. They would have tried to use any strong federal power to suppress the antislavery movement and prevent the question of slavery from ever arising. I'm not sure if this would have prevented the Civil War. The Gilded Age robber barons would eventually have amassed enough economic power to challenge the southern planters. If they avoided the slavery question, the Union might have held together until mechanized farming made slavery obsolete, perhaps during the 1940's. Northern industrialization would likely have involved more turmoil. The U.S. might also have taken over various Caribbean and Central American nations. I doubt this situation is an improvement over the real historical one.