Denmark, France and Uruguay have no slavery in 1861, and Gran Colombia and the CSA also have slavery enabled in their history files.Brazil, Cambodia, Colombia, Dai Viet, Denmark, Egypt, Ethiopia, France, Khiva, Korea, Luang Prabang, Madagascar, Netherlands, Oranje, Portugal, Paraguay, Siam, Sokoto, Spain, Texas, Tripoli, Transvaal, Uruguay, the USA and Venezuela
Shouldn't Oman have slavery?
We need definition of slavery, cause in some sense Austria/Russia had serfs who were, you know, almost a trade good. There were slaves in medieval Europe but it was banned, those were exceptions (although numerous). We have also see how did the slavery ended. If it has just faded and there weren't much slaves (and/or they were only in uncivilized regions and disappeared with civilization) there's no point to add them to specific country.
Also, there's Tibet. At least slavery was important there till Chinise came, not sure this is the case in V2.
Serfs do not count as slaves (it would be nice if serfs had been added though).
By the way, what is actual, real world difference? You can trade serfs, force them to work, beat them - what else do you need to call somebody a slave?