Justifying war is almost always difficult. It is not easy to weigh the intentions and facts in the sordid situations of international politics. Throughout history many philosophers have attempted to outline the just causes and proper means of fighting international disputes. In Western thought the development of these doctrines are marked out by Augustine and Aquinas, who were Christian philosophers and later the modern theory was developed by a Remonstrant Dutchman; Hugo Grotius (der Groot). Grotius was a scholastic and developed the modern view of the just war theory in the 16th -17th centuries through his book; De jure belli ac pacis libri tres (On the Law of War and Peace: Three books). He outlined the parameters in determining the legality and behavior of just war.
There are two important philosophical principles used when discussing just war. Jus ad bellum means Justice of war and jus in bello means justice in war. Essentially, these terms refer to the two distinct but interconnected measures of the justness in war. The questions he sought to answer were whether going to war is ever justifiable (justice of war), and once engaged in war how should war be conducted in a humane way (justice in war).”
As international law developed, a greater order was needed in the interactions of nations as they negotiated to avoid war. Furthermore, rules for conduct once engagement of military forces began brought a better sense of order to the conflict because these rules created a level of expectation regarding the conduct of the warring parties. The two principles are linked in the fact that one (jus ad bellum) outlines ethical conduct in avoiding war and the other (jus in bello) outlines ethical conduct once engaged in war.
Grotius’s rules for declaring war are 1.) countries must be injured, 2.) the country injured must respond proportionally, 3.) there should be measurable success, 4.) war must be recognized publicly, 5.) war must be declared by a legitimate authority and 6.) war must be a last resort.
Nations should use these rules when engaging in armed conflict against another nation. There is a moral legitimacy that can be lent to a cause by trying to first seek peace and avoiding rash reactions to what might be minor offenses. One can appreciate the tactical advantage of a sneak attack like Pearl Harbor but it is a cold cynical person who thinks killing, even soldiers, who are unsuspecting and unprepared is a legitimate and good thing. Using these rules can resemble a chess game and the purpose of them is to stall or avoid the shedding of blood. Of course, once war begins, the cause can be justified in the eyes of the international community by one nation strenuously attempting to avoid war.
Grotius’ rules for conducting war are 1. distinction of combatants by uniforms and only attacking recognizable distinction, 2. Proportionality is defined by damages to military targets damaged in greater proportionality to civilian collateral damage, 3. attack necessary military targets (not food factories), 4. fair treatment of captured combatants and 5. no use of evil weapons like weapons of mass destruction (nukes, gas or incendiary bombs).
Grotius’ rules ensure moral justification for war and ensure some sense of protection for the people of the warring nations, not only during war but after defeat in war.
The Stanford Philosophical Encyclopedia; http://plato.stanford.edu/entries/grotius/
International Politics on the World Stage, McGraw Hill, Rourke and Boyer. 2004.