One reason people believe that the ICC is the solution to terrorism is because they send a message that no body is above the law. The ICC was made to bring in cases from multiple different countries and regions. War criminals would be taken to an international court rather than one specifically for their own country. This is necessary because if the war criminal was especially powerful (which most of them are) they could bribe or threaten the lives of judges so that they would not be punished. But if they went to an international court, they would not be able to do this.