St Augustine
V Hrabar ‘La doctrine de droit international chez Saint Augustin’ (1932) 3–4 Archives de philosophie du droit et de sociologie juridique 428–46 Journal in Law Bod at Jurisp 300 A60
Christian Love and Just War : moral paradox and political life in St. Augustine and his modern interpreters by St Thomas Aquinas
ST 2–2, qu. 40
Summa Theologica Secunda Secundae Quaestio 40
Treatise on The Theological Virtues (Second Part of Second Part of ST) Question 40
Narrative, Nature, and the Natural Law : from Aquinas to international human rights by MPEPIL divides its into overview of the History of International Law into the following:
The Law Bod has the print copy of this encyclopedia at Internat 500 E56c, but the online version has had a number of updates since the work was printed
War and Peace in Ancient and Medieval History by 
The Social Politics of Medieval Diplomacy : Anglo-German relations (1066-1307) by 
Peacemaking in the Middle Ages: principles and practice by Google books has digitized our copy of
Ernest Nys. Les origines de la diplomatie et le droit d'ambassade jusqu'a Grotius
(1884)
Other titles available in Law Bod include