Why did post-Roman rulers abandon tax-paid army?

Question

According to C. Wickham's The Inheritance of Rome: Illuminating the Dark Ages 400-1000, pages 102-104, in 5th century rulers abandoned Roman tax-paid army in favor of medieval feudal one, which was far worse. They needed the latter to settle their adherents, but why they did not use both or revive the former a century or two later? It looks as if it would give them a great advantage.

Beginning in the fifth century, there was a steady trend away from supporting armies by public taxation and towards supporting them by the rents deriving from private landowning, which was essentially the product of this desire for land of conquering élites...

But if the army was landed, the major item of expense in the Roman budget had gone... Tax is always unpopular, and takes work to exact; if it is not essential, this work tends to be neglected... Tax was, that is to say, no longer the basis of the state. For kings as well as armies, landowning was the major source of wealth from now on...

This was a crucial change. Tax-raising states are much richer than most land-based ones, for property taxes are generally collected from very many more people than pay rent to a ruler from his public land... And tax-raising states have a far greater overall control over their territories, partly because of the constant presence of tax-assessors and collectors, partly because state dependants (both officials and soldiers) are salaried. Rulers can stop paying salaries, and have greater control over their personnel as a result. But if armies are based on landowning, they are harder to control. Generals may be disloyal unless they are given more land, which reduces the amount of land the ruler has; and, if they are disloyal, they keep control of their land unless they are expelled by force, often a difficult task.

Update (answer to Mark C. Wallace's comment): The taxes were always unpopular, which did not make Romans to change their army. Once someone with a private army conquered a piece of land, it would be natural for him not to pay the adherents from taxes, but to give them land, as it would satisfy them more; but it is strange to abandon the tax-paid army completely, because it is a big disadvantage even in the not too distant future. To consider it from the evolutional point of view, the states without tax-paid army should not survive natural selection.

Update 2 (detalization motivated by Twelfth's answer from different viewpoint). As I understand from Wickham's books, in 5th century the Western Roman Empire, with its regular paid army, disintergrated into a number of kingdoms (a couple of centuries later they became Francia, Spain, Lombardy...) based on militarized landed aristocracy. Not that it was overwhelmed by hordes of 'barbarians', who invaded or were allowed to entry, but rather that its parts changed allegiance from Rome to local rulers and switched to their ethnicity.

Roman legions for centuries were not only struggling with external enemies, but also fighting each other in civil wars, because they were paid by their generals, settled as veterans by them, and thus loyal primary to them. Generals could easily seize tax-collection and start warring with each other, but still generally looked for Rome, therefore the Empire disintegrated and integrated many times.

The situation changed in 5th century. Firstly, large parts of Roman army began to consist of 'barbarians', people coming from the border regions, either inside or outside the Empire (cultural difference was not very large after four centuries of more-or-less stable border). Even magistri militum, supreme commanders, were 'barbarians', like half-Vandal Stilicho.

Secondly, the economy of Empire was declining and localizing, therefore people became to look more to their neighbors, then to Rome. It seems natural to me if both reasons reinforce each other, but Wickham is rather vague about it.

Now, it was natural for separatist barbarian generals to base their power on ethnicity, and to their supporters to consider themselves of the same enthnicity (it was not difficult as many came from Danube border, the melting pot of nations). Thus they were transformed from revolted parts of the regular army to 'barbarian hordes', which can be settled on the land and later fight for their leaders because of their newly-obtained ethnic unity.

This description seems generally coherent, but for one thing: land-settled army made states much weaker in both economical and military sense. It can be seen on the example of the successes of Byzantine Empire fighting with many 'barbarian' kingdoms. So it seems to me that if, say, Franks saved the vestiges of tax system and returned to the paid army, they would centralize their state, avoiding the divergence of boundary regions, and have more loyal and powerful army, and conquer all their neighbors. But they would not do it for one-and-a-half millenium, until Napoleon! =)

Answer 1

"abandoned Roman tax-payed army in favor of medieval feudal one, which was far worse."

Paying an army with tax money does not confer inherently superior quality. While one could argue European feudal armies were inferior to the Roman legions, this had very little to do with taxation and much more to do with the fact that the Romans had a large, professional, standing army.

The prime factor here is the diminished state resources available to most European rulers after the fall of Rome, which necessitated the reliance on feudal levies in the first place. Therefore,

"It looks as if it would give them a great advantage."

No, it doesn't, and it wouldn't.

"but why they did not use both or revive the former a century or two later?"

Actually, they did, just not necessary right away.

Over the preceding three hundred years war had become the preserve of a body of professionals, knights for whom it was a major source of income. This state of affairs had come about gradually and, in large part, as a response to the equally slow erosion of feudal military obligation. Of the eighty-seven knights present at Caerlaverock in 1300, twenty-three were paid for their service and the rest were either members of the royal household or men responding to the traditional feudal summons.

_{James, Lawrence. Warrior Race: A History of the British at War. Hachette UK, 2010.}

The main barrier was economics. When the Roman Empire fell, the economy of Western Europe was in shambles. The continental trade that had once flourished was replaced by small, largely (though not completely) self-sufficient manors. Economic weakness, compounded by an inadequate monetary supply meant it was easier to levy taxes in kind or in the form of services, rather than money.

Nonetheless, as the money economy of Europe recovered, mercenaries became more active in the latter Middle Ages. Liege lords hired them to complement feudal levies, and vassals hired them to fulfil military obligations. In some systems, mechanisms like scutage was developed to allow a vassal to opt out of military service by paying a fee, which the king then used to to hire substitutes.

The consequent reduction of the number of feudal troops available was largely offset by a parallel increase in the employment of stipendiaries and mercenaries . . . [M]any knights themselves, though still under feudal obligation, were also paid by the end of the 13th century,

_{Heath, Ian. Armies of Feudal Europe 1066-1300. Wargames Research Group, 2016.}

In essence, scutage was a tax; and it was regularly used to pay for an army.

"Once someone with a private army conquered a piece of land . . . it is strange to abandon the army completely"

The flaw in logic here is that those "private" armies were not paid in the first place, and especially not paid by taxes. They were personal retinues who served their leader due to personal obligations. Furthermore, these originated mainly from the Germanic tribes that overran the Roman Empire, so it would have been rather more strange for them to suddenly be paid like a Roman standing army.

There's also the glaring problem of having the money to actually pay for an army. As we saw above, even knights were paid to serve longer than obligation demanded; the challenge was having the money to pay with. Up till the end of the Middle Ages, most states only hired armies when they need to.

A traditional agricultural economy was usually not rich enough to pay for a permanent army staffed with large numbers of men well equipped with expensive horses, armor, and weapons. The net result was that rulers relied on short-term armies instead.

_{Janin, Hunt, and Ursula Carlson. Mercenaries in Medieval and Renaissance Europe. McFarland, 2013.}

No medieval state in western Europe could compete with Rome's financial resources or degree of centralised control; hence none of them

"from the evolutional point of view, the states without tax-paid army should not survive natural selection."

Perhaps, but evolution doesn't work off a couple of years. Eventually all the major feudal states of Europe that survived did adopt professional standing armies paid out of general taxation.

Moreover, evolution is all about the survival of the fittest in a given environment. If the "tax paid army" was truly so superior, the Roman Empire wouldn't have fallen. In reality, maintaining such an army was a massive economic burden, which was simply not realistic in most of Europe throughout the Middle Ages.

Answer 2

And from comment to answer as it's from a much different angle than Sempahore...

They needed the latter to settle their adherents, but why they did not use both or revive the former a century or two later?

They couldn't. In this time frame, the Byzantine empire was thoroughly stretched financially from the wars in Persia (Byzantine - Sassanian wars) and later the Arabic wars. Their lands were struggling under harsh tax rates to support these armies as is and the devastation from the conflict started to impact what wealth the lands could produce. War is costly and the Byzantines were pushing a point where they could no longer afford war.

The Western Empire was even worse off...the power squabbles hit almost absurd heights and there was no longer any consistency in leadership. Most western empire emperors were somewhat contested (and in some cases not even recognized by the eastern empire) and the ones that were recognized had horribly short reigns, usually coming to death at the hands of an assassin or their own army turning on them. Tax collectors and most officials were corrupt and held little loyalty to anyone but themselves, meaning what taxes were collected rarely ended up in Roman coffers (slaying the Roman officials/tax collectors and proclaiming oneself emperor happened a few times as well, such as the Gordinians in Carthage). There were a few periods where a loyal subject of Rome that wanted to pay his/her taxes couldn't find a representative to pay taxes to. For info on how absurd this got, Year of the Five Emperors (google it for details) was an outright absurd time (193ad), yet somehow the Romans managed to outdo themselves in 236 with the year of the six emperors (I really recommend reading the intro here: https://en.wikipedia.org/wiki/Year_of_the_Six_Emperors you have a cruel tyrant, a young aristocrat revolt, an elderly emporer and his son, a jealous neighbor, riots in Rome, an army killing it's own general, and feuding co-emperors publicly put to death...all in under a year).

because it is a big disadvantage even in the not too distant future.

You would need someone to look out for the not too distant future for this to apply. Most Western Empire Roman Emperors would be looking long past their own death to see the not too distant future.

The only thing that the Western Roman empire possessed that it could support an army with was land, not money. The feudal system was very much a response to the economic state of Europe.

Answer 3

Other users' answers and comments motivated me to try answering my own question. Unfortunately, I can not give sources to my guesses, so please correct me where my speculations are wrong. Language fixing is also welcome!

First, one reason is already explained by Semaphore as "evolution is all about the survival of the fittest in a given environment". The patchwork land-settled army was enough to depend the country from external enemies, why cause internal resistance by increasing taxes? Only to conquer these enemies, but then Franks would not be much different from West Roman Empire and would face the same problems that caused it to fall (on which the historians can not agree for centuries). All the main kingdoms (Francia, Spain, Lombardia) seem to be on the maximal possible extent, with distant regions already not stable.

Second, they probably just could not do it. When Rome conquered large swaths of West Europe, these territories were economically and militarily inferior. Romans were able to build up their tax system there from scratch, as even strongest resistance would be relatively feeble. But early medieval kingdoms were more or less homogeneous; once the tax system has almost crumbled, the resistance to increasing taxes would be enormous.