Complex sentence: In addition to being covered under laws prohibiting the unlicensed practice of medicine, tongue splitting is now explicitly illegal in some U.S. states and banned in the U.S. military, so, by necessity, it is an underground practice.
Split into simpler sentences: In addition to being covered under laws prohibiting the unlicensed practice of medicine, tongue splitting is now explicitly illegal in some U.S. states and banned in the U.S. military. Thus, by necessity, it is an underground practice.