I'm not an expert, but some reading/observation reveals this:

One might say there are 3 basic forms of human captivity, with some overlap between each:

1) Indentured Servitude-The person is bound to another for a term, usually to pay off a debt

2) Prisoners of War/Prisoners of Crime-The person is bound to an enemy or bound to a term, to work off being captured or having committed a crime (with or without "rules")

3) Chattel Slavery, in which humans are property that can be sold, with little or no rights.

I believe that in the Americas, captive labor was generally indentured (some black but mostly white) until the Barbadan Slave Code of 1661, adopted in S Carolina in 1696 (both of which formalized chattel slavery, which more or less began to replace indentured servitude). Of course this ended here with the 13th,14th, and 15th Amendments, beginning in 1865. Until deep-South labor-intensive cotton was grown en-masse beginning in the late 1700s, the Caribbean had much greater chattel slavery demand/occurence.

The corollary is that many Native Americans were essentially sold into Caribbean slavery as war captives in the 1600s, as were West Africans (either "POW"s or "criminals" by other West Africans). This might be similar to the way Britain sent criminals/prisoners to Australia and NZ later? Of course, one man's criminal is another man's freedom fighter, but in the old days might was right. Calling a chattel slave a "POW" might have worked of some of the guilt.

My own father was a German POW, fortunately protected by the Geneva Convention and liberated by the Allies. Some of his ancestors helped run the NY underground railroad & died fighting for the Union Army to end slavery (some were Rev War/Civil War POWs). Chattel slavery is definitely the worst...the others are still around today but there is overlap in the definitions. It has occured to me that some workers are still essentially indentured servants, some prisoners essentially chattel slaves. There needs to be universal/basic protections.