Genocide
All signatories to the CPPCG are required to prevent and punish acts of genocide, both in peace and wartime, though some barriers make this enforcement difficult. In particular, some of the signatories—namely, Bahrain, Bangladesh, India, Malaysia, the Philippines, Singapore, the United States, Vietnam, Yemen, and former Yugoslavia—signed with the proviso that no claim of genocide could be brought against them at the International Court of Justice without their consent. Despite official protests from other signatories (notably Cyprus and Norway) on the ethics and legal standing of these reservations, the immunity from prosecution they grant has been invoked from time to time, as when the United States refused to allow a charge of genocide brought against it by former Yugoslavia following the 1999 Kosovo War.

Q: What major western power is exempt from charges or claims of genocide against itself?
the United States