Given that there were relatively few free persons of color and few urban slaves when compared with the vast majority of rural slaves, why is it important to understand their experiences? Explain how slavery became such a powerful yet horrific engine of economic development in the South. What made Southerners so defiantly defensive about preserving this practice? Understanding the South's viewpoint can help you understand why the Missouri Compromise was a huge deal and understand how this would lead towards the Civil War.

It is important to understand the experiences of slaves in the Union and in urban areas because this understanding will provide insights into slavery as a whole. Studying rural slavery in the Southern states exclusively will only give scholars an incomplete picture of slavery as a system of oppression and how it affected the entire United States.
In fact, one of the largest slave ports in history is Rhode Island, a northern or "Yankee" state. This shatters the assumption that only the South was involved heavily in the slave economy.
Likewise, it is important to study the history, perspectives, and social standing of free Africans and African Americans during the slavery period. Historians can gain insights into the complex dynamics of slavery and the American society at the time. Unlike Nazi Germany, which implemented a white supremacist-based genocide against a certain culture, slavery wasn't born out of racial hatred.
While white supremacist views—particularly the belief that nonwhite Christians were subhuman and second-class citizens—contributed to the inhumane justification for slavery, the slave trade itself was initiated due to capitalism. The South had a predominantly agrarian economy. There were many landowners who owned large swaths of plantations and needed an enormous amount of manpower to work the fields.
The Southern plantation owners defended their use of slaves because their livelihoods depended on it. However, many wealthy plantation owners simply became accustomed to their lifestyle and believed that owning slaves contributed to their social and economic standing. If you owned slaves, you were a made man, and this gave plantation owners social power.
Another reason why slave traders and plantation owners fought to keep slavery is because the slave trade was lucrative. Many slave traders did not capture slaves for their own plantations but to earn large amounts of profit from selling human beings. Missouri, which outlawed slavery before the Missouri Compromise, wanted Congress to allow the state to practice slavery, and in return, slavery in Maine was outlawed. This evenly balanced the amount of slave and free states.
Missouri's desire to practice slavery is an indication that states used slavery to increase their economic growth. It also highlighted the differences in the North and South's respective industrial revolutions. The North urbanized and utilized skilled laborers in factories, while the South remained agrarian and depended on a long history of slavery.