Complex sentence: Earth magic tends to be associated with white magic users, since it is more difficult to gain access to the materials necessary for black earth magic; black earth magic involves the sacrifice of animals and, in some cases, humans or Inderlanders.
Split into simpler sentences: Earth magic tends to be associated with white magic users since it is more difficult to gain access to the materials necessary for black earth magic. Black earth magic involves the sacrifice of animals and, in some cases, humans or Inderlanders.