I thought it was implied, but by "slavery" I meant "slavery in the United States, which predated the confederacy proper, which itself was made up primarily of the states that most benefitted by slavery, and that went to war to fight to maintain its practice ". Oh and of course, this slavery, which lasted for centuries in the colonies and states making up the confederacy (not just those states, but pretending it was only 5 years that could be blamed on the confederacy, when the illness was endemic in the USA, but primarily the southern states, for more than half the existence of the USA in total, is... interesting).
I would wager there is not a person in the USA above the age of 15 who has not had it explained to them, reported to them, or heard the explanation, that the confederacy fought to maintain the practice of slavery, and the confederate battle flag is directly tied to that - not to put too fine a point on it - evil regime. If you have to bring up the nazis to make the confederacy look better, you're not doing it right.