At the same time, the All-Volunteer Force has proved resistant to expansion in times of increased security need, it has also proved difficult to shrink its significant cost during periods of relative peace. As with the Roman All-Volunteer Force, the formation of a professional military has also created natural political interests opposed to measures that would have enabled even relatively ineffective spending to be cut down in peaceful years. Even in the relatively secure years of the 1990s, U.S. military spending never passed below 3 percent of GDP and declined only slightly in real dollar figures.

Yet despite the historically massive expenditure on a “peace time” military (inasmuch as the United States’ continuous global deployments may be considered “peace time”), and despite the fact that U.S. military spending remains substantially greater than any possible competitor, American policymakers increasingly face hard tradeoffs where even record budgets cannot stretch. In particular, American policymakers face severe tradeoffs between investing in present capabilities, or future capacity, where the large standing All-Volunteer Force essentially commits the United States to a focus on present capabilities even when the specter of rising competition with peer competitors like China might suggest for a capacity-focused approach.

The American All-Volunteer Force has not yet had two centuries for its doctrine to stagnate in the way that the Roman army did. Nevertheless, the all-too-eager reorientation towards large-scale combat operations (LSCO) suggests increasing inflexibility in how at least part of the United States military understands its mission. That the United States military has often had to relearn how to operate outside of LSCO is a point well-made by Nadia Schadlow in War and the Art of Governance. But a lack of institutional memory is rather a different thing from the determination that the military simply ought not to be asked to wage certain kinds of wars, documented by David Fitzgerald in Learning to Forget for example, and all but advocated by Daniel Bolger in Why We Lost. It is too early to tell if the shift back to LSCO and peer competition advocated in the 2017 National Security Strategy and seemingly also endorsed by the new Biden administration is a sign of a determination by the military establishment to become more flexible in confronting multiple kinds of missions or if it is merely a retreat back to the familiar comforts of planning for LSCO and so a sign of further doctrinal calcification.

THE GATES Commission also insisted that “the long-established institutional framework, firm public attitudes, and the similarity of future forces with or without conscription will help prevent separation between the armed forces and society.” Again, a sober look at the Roman example might have tempered such optimistic assumptions. The Roman experience offers stark warnings about the long-term impact of an all-volunteer military on the civil-military relationship. The collapse of the Roman Republic was complex, and ought not be simplified to a single cause. But the failure of the civil-military relationship as a consequence of the process of professionalization in the Roman army was a clear accelerant in the crisis.

Rome was not lacking in “long-established institutional frameworks.” By the time the Roman army began to professionalize and shift slowly towards the all-volunteer forces of the first century BC, the Romans had held to a tradition of universal male military service among the landholding classes since the foundation of the republic in 509 BC, although the exact form and structure of the early Roman army is beyond confident reconstruction.

Prior to the professionalization of Rome’s armies, there was a strong connection between the citizen body that voted for war and the soldiers who waged that war. The civil-military relationship in Rome was, as in modern democracies with conscription, rooted in the effective identity between the citizenry as a political body and the army; all of the same citizens who fought also voted and vice versa. Votes on war and peace were always held in the most formal of Rome’s voting assemblies, the Centuriate Assembly (comitia centuriata), which was itself organized by the same census class distinctions which in turn determined how citizens would serve in the army—citizens voted for war arranged exactly as they would have to fight in that war. Where the interests of the Roman people diverged from those of the Roman oligarchy, that very equivalence between soldiers and citizens could enable the citizenry to extract concessions from the elite by refusing to serve, as happened repeatedly with successions of the plebs during the struggle of the orders (494–287 BC).

Despite this long history and undoubtedly “firm public attitudes” about the sanctity of the republic, the professionalization of the Roman army in the Late Republic nevertheless had the effect of misaligning the interests and incentives of the Roman soldiery from those of either the Roman people or the Roman Senate, which, although it lacked many formal powers, was in practice the core Roman civil governing institution. This misalignment occurred against the backdrop of elevated, though not unprecedented, political tensions within the Roman Republic, concerning the extension of citizenship to Rome’s Italian allies and arguments over land reform. Much as in the United States today, many of the tense political debates of the time revolved around the perception that Rome’s rising wealth had enriched a select few while leaving many common Romans behind or even worse off.

Previous political tensions of this sort had been to a degree mediated by the fact that the citizen body and the army were so nearly identical, enabling the citizenry to extract concessions from the elite without violence by refusal to serve. That professionalization decoupled this relationship was not an unintended consequence, but (as noted above) the intended goal in order to overcome civilian resistance to conscription without having to trim Rome’s strategic ambitions (or the ambitions of Roman politicians for whom military success was a prerequisite to greater political stature). Nevertheless, it was perhaps only a matter of time before politician-generals whose political agendas were hopelessly bogged down in the political gridlock recognized the potential for using their veterans or their armies to push things through. And so, Gaius Marius was prepared, in 100 BC and later again in 86 BC, to use the veterans of his campaigns to intimidate voters and achieve with violence what he had not managed by persuasion. It was a small step until Sulla could turn his army against Rome, armed with promises of loot to be gained in the east which the troops, veterans of his campaigns in the Social Wars, might not expect if his opponents remained in power. These were examples subsequent Roman commanders would follow, exploiting the disconnect between the incentives of the soldiery and the citizenry to turn the one on the other in the pursuit of power.

Augustus was subsequently able to realign the incentives of the Roman state and soldier, but only by combining them in himself and cutting out the people altogether. Nevertheless, the distinctive culture of the army often made it difficult for “civilian” emperors to control it. The emperor Nerva was effectively compelled to select Trajan, a military man, as his heir, to satisfy the army. Septimius Severus’ dying advice to his sons, to “Be harmonious with each other, enrich the soldiers and scorn all others” spoke to the degree that the demands of the army had eclipsed the needs of the people or the state. In the event, the last emperor of Septimius’ dynasty, Alexander Severus, was assassinated by his soldiers for prudently avoiding a war which would have been costly to the treasury but enriching to the soldiery. The soldiers replaced him with an officer, Maximinus Thrax, who represented the soldiery well but whose political incompetence plunged Rome into the crisis of the third century after just a three-year reign.

Obviously, the American civil-military relationship is not in such dire straits as this, but there are more than a few troubling signs that the beginnings of the processes which eventually unmoored the Roman civil-military relationship are now underway. The recent confirmation of former general Lloyd Austin as the secretary of defense, the second former general in four years to be appointed to the post, has raised renewed concerns about civilian control of the military. While Austin has pledged to uphold civilian control of the military, it seems that the norm against appointing former members of the armed services to the position has been eviscerated by Donald Trump and Joe Biden. 

Equally concerning is the implication that presidents looking to signal their tough competence on military matters have now found that the way to do it is to appoint a former member of the military. That political strategy suggests that there is an emerging public perception that on matters of national strategy (matters that Carl von Clausewitz, in his trinity, sensibly leaves under the purview of politics and the state) former officers have a unique competence not reproducible from the civilian realm. It is a viewpoint increasingly held by members of the All-Volunteer Force themselves, an apparent consequence of the increasing isolation of volunteer personnel from the society they serve. That public perception is, in the long run, likely to be more dangerous than any individual appointment of a patriotic, public-spirited former general. After all, it is a short leap from the assumption that former officers have that unique competence to the conclusion that only such individuals ought to be trusted with such weighty decisions. Nevertheless, it remains true, as Georges Clemenceau quipped, “la guerre, C’est une chose trop grave pour la confier à des militaires” (war is too serious a matter to entrust to military men). There is a real, albeit distant, risk of national strategy becoming something decided on by military, to be carried out by the military. Past states which collapsed the corners of the trinity this way fared poorly.