In the United States, the law regarding murder is complex, especially due to the principle of "dual sovereignty" that is part of federalism. In most cases there is a hierarchy of acts, known collectively as homicide, of which first degree murder or felony murder is the most serious, followed by murder, followed by manslaughter which is less serious, and ending finally in justifiable homicide, which is not a crime at all. However, because there are at least 57 relevant jurisdictions, each with its own criminal code, this is a considerable simplification.