The Meanings of Slavery

 I'm not sure what "slavery" meant in the18th and early 19th century.  One meaning obviously was chattel slavery, where a person was enslaved, could be sold, and the status was inherited based on one parent's status.

But what was the "slavery" which the American rebels feared at the hands of the British?  What was the opposite of the , "land of the free" in the Star Spangled Banner--was that also slavery?

One thing that's true--for centuries in many different places the losers in a war might be subject to slavery, or worse.   The New England settlers sold some of their Indian captives into slavery in the Caribbean. Oliver Cromwell sold Irish captives into the Caribbean (though I don't believe their status was inheritable).  Some Native American tribes imposed "slavery" on their war captives, although it seems there was a lot of variety in the patterns. I was surprised to learn that some Pacific Northwest tribes indeed had chattel slavery.  

I've not seen any discussion of whether the rebels really feared being sent into slavery if they lost the war, or whether the use of "slavery" was similar to the current use of "slavery" in connection with socialism by libertarians.