Classic overview in print
Walker A history of the law of nations v. 1. From the earliest times to the peace of Wesphalia, 1648 (1899) Internat 510 W185c
Thirty Years' War, 1618-1648
The above is a subject search term in SOLO in its own right.
Francisco de Vitoria c1483-1546
Balthazar Ayala, 1548-1584.
Jean Bodin 1530-1596
His key publications have been translated into English:
De legationibus libri tres Internat 750 G338a (Classics of international law, no. 12) considering role of ambassadors.
De iure belli libri tres (1598) (Internat 750 G338b (Classics of international law, no. 16) 3 because he considers when war can be justified ad bellum, rules during battle in bello and the roles of law after post bellum.
De armis Romanis has been translated more recently