The colony of which European kingdom issued the first anti-slavery proclamation in America in 1654, limiting the duration of slavery to six years and setting a wage?

On May 18th, 1652, Rhode Island became the first of the thirteen colonies to ban slavery. The good intentions of those who wrote the law, however, went unheeded - the statute was largely ignored for over a century, as many merchants in the state became leading slave traders in colonial America.

The act read,

"Whereas, it is a common course practiced amongst English men to buy negroes, to that end they have them for service or slave forever: let it be ordered, no blacke mankind or white being forced by covenant bond, or otherwise, to serve any man or his assighnes longer than ten years or until they come to bee twentie four years of age, if they be taken in under fourteen, from the time of their cominge with the liberties of this Collonie."