The ICC is a court of last resort. It will not act if a case is investigated or prosecuted by a national judicial system unless the national proceedings are not genuine, for example if formal proceedings were undertaken solely to shield a person from criminal responsibility. In addition, the ICC only tries those accused of the gravest crimes.
It's also only applicable to signatories, afaik. Neither Iraq nor the United States are parties to the Rome Statute - the 104 nations. Afghanistan is, though.
Jurisdiction and Admissibility
The Court may exercise jurisdiction over genocide, crimes against humanity and war crimes. These crimes are defined in detail in the Rome Statute. In addition, a supplementary text of the “Elements of Crimes” provides a breakdown of the elements of each crime.
The Court has jurisdiction over individuals accused of these crimes. This includes those directly responsible for committing the crimes as well as others who may be liable for the crimes, for example by aiding, abetting or otherwise assisting in the commission of a crime. The latter group also includes military commanders or other superiors whose responsibility is defined in the Statute.
The Court does not have universal jurisdiction. The Court may only exercise jurisdiction if:
* The accused is a national of a State Party or a State otherwise accepting the jurisdiction of the Court;
* The crime took place on the territory of a State Party or a State otherwise accepting the jurisdiction of the Court; or
* The United Nations Security Council has referred the situation to the Prosecutor, irrespective of the nationality of the accused or the location of the crime.
The Court’s jurisdiction is further limited to events taking place since 1 July 2002. In addition, if a State joins the Court after 1 July 2002, the Court only has jurisdiction after the Statute entered into force for that State. Such a State may nonetheless accept the jurisdiction of the Court for the period before the Statute’s entry into force. However, in no case can the Court exercise jurisdiction over events before 1 July 2002.
http://www.icc-cpi.int/about/ataglance/jurisdiction_admissibility.htmlSince the US has veto power in the UN Security Council, there's virtually zero likelihood that they'd make a referral to the ICC. Some subsequent US President and administration would have to promulgate such a referral. What're the chances? (Zero or none?)