It is possible for a constitution to simply not mention it and let the legislature hash it out (like the US constitution did prior to the Civil War), rather than granting explicit permission to do slavery under explicit circumstances (like the US constitution after the Civil War).
It is also possible that the dominant social forces simply don't give a shit what some piece of paper says.
do Liberia et al not have constitutions? or just permit constitution-breaking
It is possible for a constitution to simply not mention it and let the legislature hash it out (like the US constitution did prior to the Civil War), rather than granting explicit permission to do slavery under explicit circumstances (like the US constitution after the Civil War).
It is also possible that the dominant social forces simply don't give a shit what some piece of paper says.
ah, I didn't read as "only country that explicitly permits slavery"