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As a crime under international law whether it is “committed in time of peace or in time of war,"  genocide extends beyond the framework of international humanitarian law and is distinguished by its unique stigma and precise definition. The 1948 Convention on the Prevention and Punishment of the Crime of Genocide went into effect in 1951 and has been ratified to date by 140 states. The prohibition against genocide is now recognized as customary international law and has been recognized by the International Court of Justice (ICJ) as a peremptory norm of international law, meaning that it is binding on states regardless of their conventional obligations.
To constitute genocide, the Convention requires the commission of at least one of five acts with the “intent to destroy in whole or in part a religious, racial, national or ethnic group as such."  The Genocide Convention’s definition of the crime has been incorporated into the statute of the ad hoc international tribunals and the International Criminal Court (ICC), and a better understanding of the various elements that must be met has emerged from the jurisprudence of these courts. 
What is important to note is that committing one of the enumerated acts alone is not enough; the crime of genocide requires the specific intent not to kill or ill-treat individuals but to annihilate, in whole or in part, the group to which those individuals belong. Additionally, the Convention’s list of protected persons is considered exhaustive, meaning that other targeted groups, such as women, economic or social classes and political groups, are not covered  -- this gap in the Genocide Convention is covered by crimes against humanity and war crimes, which impose liability for crimes that are waged against civilian groups that fall outside the protection of the Genocide Convention or that lack the required specific intent. Further, it is often argued that the application of the crime of genocide is properly limited so that it does not lose its powerful deterrent capabilities. 
The term “genocide” is not used in the Geneva Conventions or in their Additional Protocols, but the acts that constitute genocide also fall under the category of grave breaches of the Geneva Conventions and would be war crimes if committed in the course of an international armed conflict.  Additionally, any act that constitutes genocide and is committed in the course of a non-international armed conflict is a violation of Common Article 3 and of Protocol II. These grave breaches, or war crimes, are those violations of international humanitarian law (IHL) that incur individual criminal responsibility, including but not limited to murder, the ill-treatment of civilian populations or prisoners of war, the plunder of public or private property and devastation that is not justified by military necessity.
Crimes against humanity were originally conceived to fill in the gap in IHL in cases where the State abused its own people, but can also apply to crimes committed during armed conflicts and against enemy civilians. While crimes against humanity have been defined somewhat differently in various international instruments, they in essence include inhumane acts such as murder, torture, enslavement and persecution  that are committed as part of a widespread or systematic attack against a civilian population. Crimes against humanity thus do not need to be connected to any armed conflict  but may overlap with war crimes if they do. Crimes against humanity may also encompass acts of genocide but include a wider range of groups than genocide and many additional kinds of acts. 
Genocide, war crimes and crimes against humanity are subject to universal jurisdiction, meaning that any state has the power under international law to prosecute offenders, wherever the crime was committed and whatever the nationality of the perpetrator and victim, as long as the prosecuting state has personal jurisdiction over the defendant. The ICC and ad hoc tribunals all have been granted jurisdiction to prosecute these crimes. Within the restraints of specific elements that must be proven for each of the crimes, the choice of how to charge an individual will at least initially and often entirely be that of the prosecutor.  Given the requirements of each category, a single act or set of actions can simultaneously form the basis for charges of genocide, war crimes and several separate charges of crimes against humanity.