THE HAGUE - Genocide, of which Croatia and Serbia have accused each other before the UN's highest court, is the gravest crime in international humanitarian law - and also the most difficult to prove.
The International Court of Justice will hand down its judgement in The Hague on Tuesday in a long-running case between the two former foes for acts committed during the bitter civil wars that followed the break-up of the former Yugoslavia in 1991.
Derived from the Greek word "genos", for race or tribe, and the suffix "cide" from the Latin for "to kill"; genocide is defined by the United Nations as an "act committed with intent to destroy in whole or in part, a national, ethnic, racial or religious group."
The word was coined in 1944 by Raphael Lemkin, a Polish Jew who took refuge in the United States, to describe crimes committed by Nazi Germany during the Holocaust.
It was used for the first time within a legal framework by an international military tribunal at Nuremberg to try Nazi leaders for their cri bmes in 1945. Those accused were however convicted of crimes against humanity.
Genocide has been recognised within international law since 1948, with the advent of the UN Convention, and lists murder among a series of crimes.
The UN in 1985 recognised the 1915 killing of hundreds of thousands of Armenians as genocide.
In 1994, the Rwandan genocide in which the UN said some 800,000 Tutsis and moderate Hutus were murdered, led to the creation of the International Criminal Tribunal for Rwanda, based in Arusha, Tanzania.
It has been handing out convictions since 1998 for the crime of genocide and complicity.
The massacre of almost 8,000 Muslim men and boys by Bosnian Serb forces at Srebrenica in July 1995 during the Bosnian war, was recognised as genocide by the ICJ in 2007.
The Balkans war crimes court, the International Criminal Tribunal for the former Yugoslavia (ICTY), has convicted several accused of genocide.
Two former leaders of Cambodia's Khmer Rouge regime from 1975-79 were handed life sentences in Phnom Penh for crimes against humanity last August and their genocide trial before a UN-sponsored tribunal continues.
Sudanese President Omar al-Bashir is wanted by the International Criminal Court (ICC) on an arrest warrant for genocide related to crimes committed against Darfur's civilian population.
Since its inception in 2002, the Hague-based ICC is the only permanent independent international court able to try the perpetrators of genocide on all continents.