With the advent of large sailing ships massive human trafficking across oceans was made feasible. For three and half centuries between 16th and mid 19th centuries slavery was big income to the coffer. Even kings, queens, and sultans had their major share in the slave business.
Under modern day refinements certain human and human part trafficking are seemingly difficult to detect and apprehend hence offer rich rewards.
n.b. When my daughter was studying medicine at Bandung she complained of lack of cadaver for practical training.