The Nuremberg trials held at the conclusion of
World War II added to international law by
(1) settling boundary disputes in Europe through
arbitration
(2) placing the blame for World War II on many
nations
(3) ruling that moral and ethical considerations
do not apply in wartime
(4) establishing that high officials and individuals
are responsible for their wartime actions
I would go for (4). The trials aimed at eliminating the excuse of.."doing my duty as ordered by my superiors" in matters of war crimes in particular against humanity (genocide, extermination, violence and retaliation against civilians, etc.)