How did the Rome Statute expand war-crimes rules to cover civil wars?

The Rome Statute of the International Criminal Court (1998) was a landmark development that expanded the scope of international criminal law to include a broad range of war crimes committed during internal, or civil, armed conflicts.1

Historically, international law and the Geneva Conventions focused primarily on interstate wars. While the 1977 protocols to the Geneva Conventions attempted to address internal conflicts, they failed to successfully expand the concept of "grave breaches"—the most serious war crimes—to include acts committed in civil wars. States were traditionally more willing to accept international oversight for interstate conflicts than for domestic ones.12

However, by the mid-1990s, international consensus shifted due to the influence of the human rights movement and global outrage over atrocities in the civil conflicts of the former Yugoslavia and Rwanda. Reflecting this evolution, the Rome Statute formally recognized that individuals could be held criminally responsible for war crimes occurring within internal armed conflicts, closing a significant gap in international legal protections.1