Due to the increased implementation of slave codes, which emphasized differential treatment between Africans, and the white workers and ruling planter class, the island became increasingly unattractive to poor whites. Black or slave codes were implemented in 1661, 1676, 1682, and 1688. In response to these codes, several slave rebellions were attempted or planned during this time, but none succeeded. Nevertheless, poor whites who had or acquired the means to emigrate often did so. Planters expanded their importation of African slaves to cultivate sugar cane. One early advocate of slave rights in Barbados was the visiting Quaker preacher Alice Curwen in 1677: " "For I am persuaded, that if they whom thou call'st thy Slaves, be Upright-hearted to God, the Lord God Almighty will set them Free in a way that thou knowest not; for there is none set free but in Christ Jesus, for all other Freedom will prove but a Bondage."