Under international law set by the Nuremberg precedent, crimes against humanity are distinguished from mere domestic crimes by virtue of their "scope," or "mass nature." Mass nature is defined by two criteria: (1) a large number of victims; and/or (2) a systematic state policy. Massacres also have a mass nature, but their tendency to happen via police action and/or under martial law usually make them count as war crimes (but see Prof. Kuper's 1981 notion of "genocidal massacre" which counts small-scale massacres as genocides). In addition to having the character of a mass nature, in order to qualify under international law as a crime against humanity, it must be shown that the targeted groups -- social groups, political groups, racial groups, religious groups, or other groups -- were targeted for mass murder because of their status as a group. According to some who equate mass murder with genocide (e.g., Gellately & Kiernan 2003), an act of genocide constitutes a crime against humanity, i.e., any use of the terms "genocide" or "mass murder" automatically imply all the Nuremberg criteria for a crime against humanity are fulfilled. However, it was not until 1948 that the term "genocide" found its way into the vocabulary of international law via the Convention on the Prevention and Punishment of the Crime of Genocide which didn't go into effect until 1951, and then only after extensive lobbying by Polish lawyer Raphael Lemkin. The US didn't become a signatory until 1988, and then only after adding a proviso that it was immune from prosecution without its consent, a proviso copied by 50 Other Nations which are Nonparties to the Convention. There are different ways different scholars have approached the definition of genocide (e.g., Harff's 1984 concept of "politi-cides;" Chalk & Jonassohn's 1990 sociological definition of "one-sided mass slaughter;" Rummel's 1997 concept of "democide" or government-sponsored killings other than capital punishment; and Power 's 2003 "race-murder" conception). Additional terms that can be found in the literature are ethnocide (a term commonly used by sociologists of race relations), culturecide (an anthropological term for the disappearance of a culture), and the phrase "cultural genocide" which presumably refers to the attempt to destroy the cultural heritage of a people. However, the 1948 Convention defines genocide as follows:
killing members of a group
causing serious bodily or mental harm to members of a group
Deliberately inflicting on a group conditions of life calculated to bring about its physical destruction in whole or in part
imposing measures intended to prevent births within a group
forcibly transferring children of the group to another group
http://www.apsu.edu/oconnort/3040/3040lect06.htm