On Outlawing War
For much of human history, the idea that war could be regulated was inconceivable. It was assumed that states would pursue their interests in foreign affairs however they desired. If a powerful state wished to conquer a foreign nation, and had a strong enough army to do so, they could invade without having to worry about a legal justification. Thucydides captured the spirit of the age when he wrote in his History of the Peloponnesian Wars that, in international relations, "the strong do what they can, and the weak suffer what they must."
It is easy to understand why the ancients came to the conclusion that war was fundamentally ungovernable. Laws were designed for political communities. To be effective, they required courts and juries and enforcers. None of these were present on the world stage. It was hard to imagine a prince obeying rules supposedly laid down for them by other city-states or nations. And if they broke the supposed law of nations, what consequences could they possibly face?
Most commentators on the history of international law skim over antiquity and the Middle Ages and begin their discussions in earnest in the seventeenth century, when international law really began. In the midst of the sanguinary Thirty Years War that brought devastation to Europe, a Dutch lawyer and historian and named Hugo Grotius published an influential treatise entitled On the Law of War and Peace. In it, he argued that in fact there was such a thing as a law of nations and that it bound sovereign states. He asserted that natural law contained within it rules for when states could go to war, and it was possible to distinguish between just and unjust wars. If a state launched a war of aggression, it was breaking the law. This of course didn't mean that it would be punished--just as not all criminals are punished--but it did mean that it was acting unlawfully.
Grotius's work marked the beginning of a centuries long effort to find legal mechanisms for ending international conflict. These culminated in 1928 in the Kellogg-Briand Pact, an international treaty that purported to outlaw warfare entirely. It was a simple agreement, containing just two operative provisions:
ARTICLE I: The High Contracting Parties solemnly declare in the names of their respective peoples that they condemn recourse to war for the solution of international controversies, and renounce it, as an instrument of national policy in their relations with one another.
ARTICLE II: The High Contracting Parties agree that the settlement or solution of all disputes or conflicts of whatever nature or of whatever origin they may be, which may arise among them, shall never be sought except by pacific means.
All the great powers of the day signed the treaty, including the United States, Britain, France, the Soviet Union, Germany, Japan, and Italy.
Students of history know what happened next. A decade after the world outlawed war, it began a new one of unprecedented violence and scale. German dictator Adolf Hitler had no intention of pursuing his dual aims of continental domination and racial purification through "pacific means," and the Second World War was the result.
One might have thought that the Second World War would put the nail in the coffin of international law. If anything could prove that treaties weren't worth the paper they were written on, it was the fate of the Kellogg-Briand Pact. Perhaps the ancients had been proven right--the laws fall silent when war begins.
But this was not what happened. During the course of the war, the Allies regularly spoke about the actions of the Axis as "crimes," and they developed a plan for holding the principal perpetrators liable. In 1945, at the end of the war, they created an International Military Tribunal at Nuremberg to place Nazi leaders on trial.
Robert Jackson, a sitting Supreme Court justice who took a leave of absence to become the chief American prosecutor at Nuremberg, opened the trial by explaining the stakes:
The wrongs which we seek to condemn and punish have been so calculated, so malignant, and so devastating, that civilization cannot tolerate their being ignored, because it cannot survive their being repeated. That four great nations, flushed with victory and stung with injury, stay the hand of vengeance and voluntarily submit their captive enemies to the judgment of the law is one of the most significant tributes that Power has ever paid to Reason.
In other words, might does not make right. Not any more, and not under the law of nations. So long as powerful countries remain committed to justice, law can prevail over war.
