As I understand it the Confederacy did declare themselves a country independent of the United States. The consequences at the time in the shape of war were appalling, and so was the aftermath of that war over a century and more, in the shape of continuing oppression of black Americans.

Perhaps it might have even been better if secession had been permitted. Perhaps slavery would have been ended in other ways, as happened over the following decades in other American countries such as Brazil. Nobody can ever know things like that.

The Confederate flag does of course have associations with slavery, and also with the oppression of black Americans over the years after slavery ended. But so does the flag of the United States. It's a guilt and a shame that has to be accepted and can be used positively, but only when it is accepted. And the same kind of thing is of course true of the flags of many, maybe most, countries.