Contra jus belli
Defined in 2 dictionaries — Ballentine's (1916), Black's (1910)
Ballentine's Law Dictionary
James A. Ballentine · 1916
Against the laws of war.
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
Lat. Against the law of war. 1 Kent, Comm. 6.
Defined under Contra in Black's Law Dictionary.