The three basic categories of international crimes were defined in the Nuremberg Trials of Nazi officials. However, because the Nuremberg Tribunals only tried citizens of Axis nations for crimes against Allied or neutral states, their moral authority was greatly weakened.
The ICC complements the International Court of Justice (ICJ), which tries civil cases.
One other country to do this has been Sudan.
India, Indonesia, Pakistan, and China have never signed the treaty; Russia, Egypt, and Israel have signed it, but not ratified it.