The Belgian missionary Louis Hennepin was picnicking on the banks on the Mississippi on 12 April 1680, when he 'suddenly perceived fifty bark canoes, conducted by 120 Indians, entirely nude, who descended this river with great speed.' Hennepin was captured by warriors of the Sioux Indians. His captors considered him 'a slave captured in their enemies' territory.' Hennepin had to perform forced labour, farming with women and children on a nearby island. The Sioux and many other First Nations in North America practiced slavery before the European invasion, but none exploited slave labour on a large scale.
From: Brett Rushforth, Bonds of Alliance. Indigenous and Atlantic Slaveries in New France (Chapel Hill 2012) Call no 2012/1449.