Complex sentence: Some priests, like Bartolome de las Casas actually invoked humanitarian reasons to replace native labor force with black slaves, alotugh later, retracted, after he saw how black slaves were treated.
Split into simpler sentences: Some priests, like Bartolome de las Casas actually invoked humanitarian reasons to replace native labor force with black slaves. Bartolome later retracted of his earlier opinions, after he saw how black slaves were treated.