According to the doctrine of State sovereignty each State has the right to exercise its jurisdiction over crimes committed in its territory-known as the territoriality principle. Even if the crimes committed are of a type that affects the international community as a whole, States are often hesitant to have their own nationals tried by an international judicial organ. History demonstrates that States rarely waived this right, which is inherent to their sovereignties, and did not rely exclusively on international justice. Rather they always preferred to exercise their jurisdiction exclusively, and only occasionally, when coerced by special circumstances, have they accepted international intervention. In order to create an international criminal court to punish grave crimes of an international character, this historical obstacle had to be overcome. The compromise reached is the principle of complementarity. This principle requires the existence of both national and international criminal justice functioning in a subsidiary manner for the repression of crimes of international law. When the former fails to do so, the latter intervenes and ensures that perpetrators do not go unpunished.
Mohamed M. El Zeidy,
The Principle of Complementarity: A New Machinery to Implement International Criminal Law,
Mich. J. Int'l L.
Available at: http://repository.law.umich.edu/mjil/vol23/iss4/3