Slavery was not introduced to the New World by Columbus. Rather, slavery was common even among native people in the Caribbean.
Columbus sought to be kind to the natives because he knew that they would be an essential component in not only his survival, but the survival of the men that accompanied him as well. When Columbus left Spain in 1492, in search of a faster and safer route to Asia, slavery was permissible. Spain did not formally ban the slave trade to its colonies until 1817 – more than 300 years after Columbus’ death.
See also this, about Samuel Eliot Morison’s Admiral of the Ocean Sea. Always good to be informed.