Final answer:
The most fervent opponents of the Thirteenth Amendment were Southern states and individuals heavily invested in slavery, fearing economic and social change. Their opposition was evident in the creation of Black Codes to circumvent the amendment's intents.
Step-by-step explanation:
The group of people most opposed to the Thirteenth Amendment were those who lived in the Southern states, particularly the former Confederate states and those who had substantial investments in the institution of slavery. The Thirteenth Amendment, ratified at the end of the Civil War, officially made slavery and involuntary servitude unconstitutional and differed significantly from the Emancipation Proclamation by permanently banning slavery throughout the United States. Southern opposition to the amendment was based on the fact that slavery was an integral part of the region's economy and social order. Many Southerners feared the economic effects of losing their enslaved workforce and the possibility of social upheaval following the emancipation of millions of African Americans. Furthermore, it was this group of people who went on to create restrictive laws known as the Black Codes with the intent to circumvent the amendment and maintain a racial hierarchy.