Customary international laws are the aspects of international law that derive from custom. Customary international law is a marriage between general principles of law, treaties and custom which is considered by the International Court of Justice, jurists, the United Nations, its members countries are the main sources for international law. Laws regarding war were an issue of customary international laws before it was codified during the Hague Conventions and the Geneva Conventions. Most world government accept customary international law, in principle if not in theory. However, there is a great deal of dissention regarding what customary international law is comprised of. In the Statue of the International Court of Justice, the existence of customary international law is agreed upon and it has been incorporated into the United Nations Charter.
Customary international laws are agreed upon with widespread repetition by states of similar international acts over time, acts must also occur out of a sense of obligation, and lastly acts must be taken by a majority of states.
Customary international law also takes into account the idea of a peremptory norm which is a rule of international law or principle which is generally acknowledged by a large number of people and typically considered binding by the international community. The basic norms under this type of customary international law usually include regulations on the use of force, crimes against humanity, war crimes, piracy, genocide, and slavery.
A large basis for customary international law was the Universal Declaration of Human Rights. While the UDHR is not always considered a legal document, it has a great deal of influence on customary international law which is something that member states of the United Nations must abide by. Furthermore, resolutions passed by the General Assembly, pending approval from the permanent members of the Security Council, can also be incorporated into customary international law.
Customary international law is a very important concept as it is the guidelines that are followed by the International Court of Justice and member states are held to these laws. These set of laws are essentially the laws of the world and despite any disagreements surrounding laws, it is absolutely to have laws that transcend borders as there are crimes that occur which cannot be tried in national courts or are committed by officials who in many poorly constructed and corrupt governments find themselves to be invincible.