Classic terminology is to consider the problem in three parts "ad bellum" (in what circumstances can war be justified?), "in bello" (what rules to apply during combat) and "post bellum" (what can be done to alleviate the aftermath)
Subject search terns to use in SOLO
War (international law)
War, maritime (international law)
International humanitarian law
Just war doctrine -- History of doctrines
Just war doctrine
Jus ad bellum
Jus in bello
Jus post bellum
Normative Approach to War : peace, war, and justice in Hugo Grotius by 
War and the Law of Nations by 
History of the Laws of War (3 volumes) by The international judicalization of the excesses of war (war crimes trils) only became significant feature of international law in the 20th century.
The Art of Making Peace lessons learned from peace treaties by 
Peace Treaties and International Law in European History: from the late Middle Ages to World War One by Articles include the following:
Great Peace Treaties (The non-Westphalian Peace; The Peace of Utrecht and the Balance of Power; The Congress of Vienna (1814–1815); The Peace of Breda (1667); The Peace of Brest-Litovsk (3 March 1918); 11.11.11: The End of the First World War on the Western Front)
International Law and the Law of Neutrality (The Treaty of Washington and Neutrals’ Duty of Due Diligence)
The Nature of Peace Treaties (Wiping the slate clean… for now: Amnesty in early-modern peace treaties; From Hostage to Fortune to Prisoner of War Splitting the Distance; Perpetual Peace; Restitution in Early-modern Peace Treaties: The Case of the Dutch-Spanish Peace Treaty of Münster (1648)—Part I; Restitution in Early-modern Peace Treaties: The Case of the Dutch-Spanish Peace Treaty of Münster (1648)—Part II; Reprisals in Early-Modern European Peace Treaties)