Who's behind Genocides, and ethnic cleansings?

Genocide, the deliberate and systematic destruction of a group of people because of their ethnicity, nationality, religion, or race. The term, derived from the Greek genos (“race,” “tribe,” or “nation”) and the Latin cide (“killing”), was coined by Raphael Lemkin, a Polish-born jurist who served as an adviser to the U.S. Department of War during World War II.

Although the term itself is of recent origin, genocide arguably has been practiced throughout history (though some observers have restricted its occurrence to a very few cases). According to Thucydides, for example, the people of Melos were slaughtered after refusing to surrender to the Athenians during the Peloponnesian War. Indeed, in ancient times it was common for victors in war to massacre all the men of a conquered population. The massacre of Cathari during the Albigensian Crusade in the 13th century is sometimes cited as the first modern case of genocide, though medieval scholars generally have resisted this characterization. Twentieth-century events often cited as genocide include the 1915 Armenian massacre by the Turkish-led Ottoman Empire, the nearly complete extermination of European Jews, Roma (Gypsies), and other groups by Nazi Germany during World War II, and the killing of Tutsi by Hutu in Rwanda in the 1990s.

Defining genocide: the Nürnberg Charter and the genocide convention
In his work Axis Rule in Occupied Europe: Laws of Occupation, Analysis of Government, Proposals for Redress (1944), Lemkin noted that a key component of genocide was the

Criminal intent to destroy or to cripple permanently a human group. The acts are directed against groups as such, and individuals are selected for destruction only because they belong to these groups.

In contemporary international law the crime of genocide is part of the broader category of “crimes against humanity,” which were defined by the Charter of the International Military Tribunal (Nürnberg Charter). The charter granted the tribunal jurisdiction to indict and try the leaders of the Nazi regime for inhumane acts committed against civilians, as well as for acts of persecution on political, racial, or religious grounds; in so doing, it also contributed to the international criminalization of other forms of abusive conduct. The momentum created by the Nürnberg trials and the ensuing revelations of Nazi atrocities led to the passage by the United Nations (UN) General Assembly of Resolution 96-I (December 1946), which made the crime of genocide punishable under international law, and of Resolution 260-III (December 1948), which approved the text of the Convention on the Prevention and Punishment of the Crime of Genocide, the first UN human rights treaty. The convention, which entered into force in 1951, has been ratified by more than 130 countries. Although the United States played a major role in drafting the convention and was an original signatory, the U.S. Senate did not ratify it until 1988.