Definition - What does Peremptory Norm mean?
Peremptory norm refers to legal principles that are considered "norms" in international law. Such norms include rules like no nation is allowed to commit genocide, have slave trades, have maritime piracy or practice torture.
Treaties or agreements made by nations in violation of peremptory norms are considered to be illegitimate and automatically void.
Justipedia explains Peremptory Norm
Any nation that attempts to violate a peremptory norm can face legal consequences.
Peremptory norms were set up because the actions that they prohibit were deemed to be so obviously immoral and heinous that it should be normal for every nation to reject them.
In the past, violating peremptory norms has caused wars to occur. For example, Nazi Germany committing genocide against the Jewish people in Europe was largely to blame for causing World War II.