One of the most telling examples of the relationship between slavery and the economy is that in 1860, four million Black people were enslaved. Black people were worth more than every bank, factory, and railroad combined. The four million Black people were worth more than all the manufacturing in this country before the Civil War began.
Without the labor of enslaved people, the free labor of millions of people over the course of two and a half centuries, the United States does not exist as a global economic superpower. It's that simple. We cannot dissent our rise to global economic superiority from the fact that millions of people worked for free for more than two centuries.
That had an impact not only on the Southern economy but the Northern economy. Capital and resources were what allowed the slaveocracy of the South to continue to flourish. There was an investment across the country in the perpetuation of slavery. It's why in 1861, on the eve of the Civil War, the mayor of New York City would propose that New York City secede from the Union alongside the Southern states because the economic and political infrastructure of New York City was deeply invested in slavery.