While there was slavery in the past in European nations as well, it wasn't as rampant as it was in the United States where there were a lot of plantation owners who also owned multiple slaves and whole families at times - before this was made illegal during the US civil war.
Answer:
abolitionists.
Explanation: The group in 19th century America that would likely be the most receptive audience for "What to the Slave is the Fourth of July?" would be abolitionists.
Find out more information about abolitionists here: brainly.com/question/6788111
