Is the ICC meant to replace national courts?

No. The ICC does not replace national criminal justice systems; rather, it complements them. It can investigate and, where warranted, prosecute and try individuals only if the State concerned does not, cannot or is unwilling genuinely to do so. This might occur where proceedings are unduly delayed or are intended to shield individuals from their criminal responsibility. This is known as the principle of complementarity, under which priority is given to national systems. States retain primary responsibility for trying the perpetrators of the most serious of crimes.