How do great powers go to war with each other? Although the vast majority of conflicts in history are fought between immediate neighbors, great powers do not always share a common border. This includes not just those protected by bodies of water, like Britain, Japan, or the United States, but also historic land rivals such as France and Austria. There are inevitably several potential scenes of conflict, forcing planners to decide where and how to commit forces: indeed, choice of theater is one of the most fundamental questions of strategy.
This, however, places strategy in a very awkward relationship with war aims. Military strategy is supposed to accomplish the objectives set forth by political authorities. Yet once initiated, hostilities take on a logic of their own; the scope of the conflict easily expands beyond its envisioned horizons, changing the goals of the war with it.
War Aims and Strategy
There is no more spectacular illustration of this than the Hundred Years’ War. Although it is commonly portrayed as a dispute over the inheritance of the French crown, that question was not brought up until several years into the war. The real point of contention was Gascony in southwestern France, which Edward III held in fief from the French king, who was trying to expropriate it by various legal devices. Given the relative balance of power, the only way Edward could hope to protect Gascony was by threatening France along its vulnerable northern border. To this end, he subsidized the princes of the Low Countries and Rhineland to contribute to a massive invasion force.
This amounted to an illegal war of aggression against his overlord. The only way he could justify it was by claiming the crown of France for himself; it was at this point that he pressed his claims. The ensuing war lasted two decades before the first peace treaty, during which the heaviest fighting occurred in the north. In a very direct way, the operational possibilities of another theater determined the nature of the war itself.
The Japanese faced a similar dilemma in World War II. Embargo by the United States left the Dutch East Indies as the only available source for oil to continue the war in China. They knew that an invasion would draw America into the conflict, so their only choice, as they saw it, was a preemptive attack on Pearl Harbor. The strategy necessary to accomplish their initial war aims, in other words, demanded much broader war aims.
The Theory of Victory
It is easy to point to these as examples of bad decisions by political leaders who embroiled their countries in wars for which they were entirely unprepared—as indeed they did. But this obscures the fact that since the time of Napoleon, Western great power wars have lasted until one side surrendered, with very few exceptions.1 It is only by accepting the most extreme scenario from the get-go that planners avoided the escalating dialectic between political objectives and strategy.
Yet even then, the true cost of victory was hard to foresee. The wider the scope of a war, the more unpredictable it becomes; it is difficult to foresee how changes in one theater will change the calculations in all others, and how that will affect the overall outcome of the war. It becomes difficult to formulate a theory of victory, in other words.
Consider the case of strategic bombing during World War II. There were many approaches put forth by airpower advocates: attacking factories to reduce production, attacking the transport networks to prevent equipment from reaching the front, attacking the cities to terrorize the civilian population into submission. These held in common a promise to end the war much quicker.
None of them worked quite as imagined. Although the bombing of factories did eventually degrade German production enough to have a meaningful effect, its most important consequences were completely unforeseen: the destruction of the Luftwaffe as an effective fighting force and the diversion of German manufacturing capacity into air defenses.
Yet the unforseeability does not mean the policy was unwise. Judging the question without the benefit of hindsight, we can say that strategic bombing made sense simply because it offered the one theater where the western Allies could actually bring its strengths to bear against Germany. Specifically, it allowed them to make use of their vast advantage in aluminum, petroleum, and manufacturing capacity, as well as their unsinkable aircraft carrier off the coast of Europe. The war was ultimately one of attrition, and the air campaign gave the Allies the opportunity to fight it.
Compare this to Rommel’s campaigns in North Africa: these only could have benefitted Germany if they had succeeded in closing the Suez Canal. Failing that, his presence gave the Royal Navy and Air Force a prime opportunity to inflict disproportionate losses on Axis shipping at the cost of comparatively small losses to British land forces.2
We can also compare this with the Western Theater in the American Civil War. For all that Sherman hoped to crush Southern morale with his March to the Sea, it did not spare the Union a grinding string of campaigns in the Eastern Theater to occupy Richmond and force Lee’s surrender. It was, in other words, no more effective than strategic bombing in accomplishing its stated aims—useful insofar as it allowed the North to apply its material and manpower advantages, diverting Southern forces from the decisive theater and wearing down their material base. They could be wrong in theory but right in practice, so long as the attrition ratios were favorable.3
This use of secondary theaters was much better understood in the long, exhausting European wars of the 17th and 18th centuries, where the eventual peace was shaped by who held what territories when the war became financially unsustainable for both sides. The Thirty Years’ War saw frequent campaigning on enemy territory with the sole intention of tying up enemy troops while living off his lands. This also made the Rhineland a favorite target of later armies, even when there were no strategic objectives to be obtained. Any towns or fortresses captured in these secondary theaters could moreover be used as chips at the negotiating table—outside the main theater of interest, strategy had an overtly open-ended character.
The Frustrated Middle
Every so often, the usual pattern is inverted. The primary theater becomes so deadlocked that secondary theaters offer a chance at decision. This happened during the War of the First Coalition: by 1796, the main Rhine theater had become a stalemate, but France emerged triumphant owing to Napoleon’s astounding success in Italy.
This is a rare exception, however, and was certainly not the intention of French war planners. More deliberate attempts to bypass the main front usually end in failure: Churchill’s plans during both World Wars to attack the “soft underbelly” of Europe struck against a rock-hard breastplate in Turkey, Greece, and Italy. Planners usually have good reason for what they consider the main theater.
At the level of grand strategy, secondary theaters are favored for somewhat different reasons. The staggering cost of war between great powers is a strong disincentive to open conflict, diverting their energies into proxy conflicts and other forms of competition. This was certainly true during the Cold War: Americans and Soviets fought directly and indirectly across Asia, Africa, and South America, but never in central Europe. In an earlier age, open hostilities between European powers were often preceded by actions in the colonies or skirmishes at sea, as happened between the British and French in the lead-up to the Seven Years’ War.
These secondary conflicts are rarely decisive in the scheme of the larger geopolitical contests. It is precisely their unimportance gives statesmen the chance to resolve conflicts without getting embroiled in an all-consuming conflagration, in tacit recognition of the runaway feedback loop between war aims and strategic decision-making.
Strategic Planning
As murky as strategic forecasting can be, the operational factors can often be planned in great detail. US Marine officer Pete Ellis was able to foresee the demands of an amphibious campaign against the Japanese as far back as the 1920s, when he laid the groundwork for the island-hopping campaign. France, Germany, and Britain spent the interwar years contemplating the particular questions of combat in the plains of northern France and Lorraine. Two centuries earlier, their predecessors spent times of peace building massive chains of fortresses along those same vulnerable frontiers.
Today, the Taiwan Strait is the subject of endless wargames and procurement debates over a hypothetical conflict, just as the Fulda Gap and North German Plain once were. It is the one flashpoint that both American and Chinese planners feel they must be prepared for, the irony being that the more it is planned for, the less likely it is to be fought. This is not to rule it out, of course, only to say that proxy wars are far more likely. It is by looking at those preparations that do not fit the mold of a Taiwan scenario that we can guess where those conflicts might be.
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The exceptions are Crimea, Austria-Prussia, and Korea. World War I is technically an exception, but hardly so in reality.
As much as Rommel is criticized for overstretching his means, the German High Command’s strategic vision for the North African campaign was hardly any better: they merely wanted to shore up their Italian allies, which exposed them to all the risks without even the hope of accomplishing anything more.
We should distinguish secondary theaters from two main theaters that complement each other. After the March to the Sea, Sherman’s Carolinas campaign formed one of the two closing jaws that compelled Confederate surrender—neither his army nor Grant’s could succeed on its own. Likewise, the French traditionally threatened Austria in northern Italy and from the Rhine, while the Austrians attacked France from the Rhine and the Low Countries. Any of these theaters had the potential to be decisive, but that required artfully balancing forces to achieve a breakthrough in one theater while frustrating the enemy’s designs in all others.