The correct answer is option 4: Cambodia. The Khmer Rouge atrocities refer to the acts of violence, genocide, and human rights abuses committed by the Khmer Rouge regime in Cambodia from 1975 to 1979.

Option 1, South Africa, is not correct. South Africa has a different historical context and is known for apartheid or racial segregation rather than the Khmer Rouge atrocities.

Option 2, Iraq, is also not correct. The atrocities in Iraq mainly pertain to events like the Iraq War, the rule of Saddam Hussein, and conflicts with terrorist groups like ISIS.

Option 3, Libya, is also incorrect. Libya faced its own set of conflicts and human rights abuses during the regime of Muammar Gaddafi and the subsequent civil war, but it does not relate to the Khmer Rouge atrocities.

In conclusion, the Khmer Rouge atrocities specifically relate to the historical events that took place in Cambodia under the Khmer Rouge regime from 1975 to 1979, where millions of people were subjected to forced labor, torture, executions, and mass killings.