It exists in some, not all. It is generally technically illegal even where it exists.
Unless we're talking informal slavery, as of female and child "sex workers," and if we're going to count them we have lots of slaves in this country.
But its existence here is a result of this nation's increasing secularization.
OTOH in Islam slavery is acceptable because it is based on their code. It is acceptable and even an honored tradition as it has always been practiced on those who are not muslim.