The wisdom of preventive war, or military action designed to eliminate a threat before it materializes, has been a subject of intense debate. Was the war in Iraq justified? And of more immediate concern, is an Israeli military strike against Iran advisable?
The arguments against preventive war are compelling. These actions rely on accurate intelligence concerning the intentions and capabilities of the targeted state. It is a dangerous precedent -- potentially destabilizing -- and has been used to mask ulterior motives or to justify aggression.
Despite these objections, at least one case for preventive war is worthy of consideration. In 1933, Adolf Hitler became chancellor of Germany. Since he had openly declared his desire to repudiate the Versailles Treaty, rearm Germany, and seize land necessary for German "living space," it was not unreasonable to assume that the Nazi regime was intent on military conquest. Yet as soon as he gained power, Hitler began preaching peace. At international forums, the Germans proclaimed they were only seeking equality with fellow nations, and that as soon as their legitimate grievances were adjudicated, they would live peacefully with their neighbors.
Although Hitler had made numerous statements to the contrary, the Great Powers (Britain and France) were fearful of provoking Germany. Rather than point out contradictions and blatant treaty violations, they preferred to be officially ignorant of obvious facts. Instead of collective resolve, Hitler was treated to appeasement, a policy that allowed him to advance preparations for what would be the greatest tragedy in history.
However, one prominent European statesman not only recognized the Nazi threat, but was also determined to do something about it. Józef Piłsudski, the leader of the Polish state, had ample experience with the aggressive tendencies of his neighbors. Germany and Russia had conspired to partition Poland in 1795, leading to over a century of enslavement before the country was liberated in the aftermath of WWI. For well over a decade, Piłsudski had seen Europe's collective security system erode, and noticed that his ostensive allies were becoming increasingly willing to abandon Poland to avoid conflict with Germany.
Having observed countless international conferences where German demands were satisfied, only to be met with new delays and grievances, he recognized that the Nazi's regime was not acting in good faith. He knew Germany was bent on regaining her "lost" Polish lands. Piłsudski believed Hitler was pursuing what appeared to be peaceful policies as a means of advancing his revisionist agenda only because he lacked, for the time being, the military means to accomplish his goals. Ultimately, the Nazi threat could only be stopped by force, or at least the credible threat of force. Piłsudski was not opposed to peaceful resolutions; he just doubted they were possible in this case, and viewed an attack on Germany as a justifiable defense of the Polish state.
Recognizing that Hitler was immune to normal diplomacy, Piłsudski began preparations for a preventive war. Unlike the situation in 1939, in March 1933, Poland was in a position to carry out this threat. As Hitler knew, the Polish army possessed more than 250,000 highly trained and well-equipped soldiers. Although in the initial stages of secretly rearming, in 1933 the German military had no modern weapons, namely airplanes, tanks, or armored cars, and according to the terms of the Versailles Treaty its army was limited to 100,000 men. Piłsudski was prepared to send Polish troops to occupy Danzig, East Prussia, and possibly Upper Silesia, while France would march through the Rhineland into the Ruhr. The move would expose the weakness of the boisterous young Nazi regime, humiliate Hitler, and possibly remove him from power. The occupying troops would then refuse to evacuate German territory until the Reich made assurances to honor the peace treaty.
While the details are murky due to his preference for secret diplomacy, according to some reports Piłsudski made this proposal on several occasions to the French, but was repeatedly rebuffed. France would not act without Britain, and the British not only refused to participate, but intimated they might support Germany if Poland was determined the aggressor.
In the end, the preventive war against Germany never materialized. But Piłsudski, who had defeated the Red Army without Western assistance in 1920, was apparently prepared to ignore international consensus and order unilateral action to defend the Polish state. Significantly, Hitler -- who understood Piłsudski was not prone to issue empty threats -- believed this to be true. Poland used the threat of preventive war to maneuver Germany into a series of agreements designed to buy time to prepare for the inevitable war Piłsudski saw coming.
Unfortunately, the Polish leader died in 1935. Poland, which had lost its brief military superiority, was attacked and overwhelmed by Germany in 1939. It will never be known if Piłsudski's preventive war could have eliminated the Nazi threat. What is known is that without it, millions of Poles were killed and the survivors condemned to another half century of enslavement.
Justification of preventive war is by its nature counterfactual; in other words, it is based on events that did not occur. Such action is perhaps particularly difficult to justify if it's successful. By definition, the original threat would have been eliminated. But just because counterfactual historic arguments are inherently controversial, it does not mean they are never valid. One can make the reasonable case that preventive war against Hitler in 1933 would have altered history in a positive direction and might have spared Europe from the nightmare of WWII.
Preventive military action should be viewed with a healthy skepticism and used as a measured response to a defined imminent threat. It goes without saying that it should only be used after reasonable diplomatic efforts have failed. But just as in the case of Germany in 1933, the consequences of failure in Iran today are enormous and warrant keeping all options -- even preventive war -- on the table.