Why did monarchy become common practice after the fall of Rome?

Question

Why did the government of most nations after the fall of Rome and the beginning of medieval age turn to monarchy?

Before the fall of Rome most nations seem to be organized after different model and few seems to embrace the practice of one person with absolute power. The Rome had Senate and/or an Emperor. The Greek (some at least) had democracy for free men. Germanic nations had councils or a chief that was part of a confederations. So how did we go from a system of so many different government types to monarchy dominating Europe?

Answer 1

The short answer is that it didn't. Monarchies did not become more common, and Europe in general did not adopt absolutist rule, immediately after the fall of Rome.

First, to answer your literal question, monarchies were already common before Rome fell.

• Imperial Rome was itself a monarchy, even though the imperators were initially careful to maintain the illusion of the Republic.
• Brythonic Britain were ruled by many petty kings, such as Queen Cartimandua of the Brigantes or King Cunobeline of the Catuvellauni, and other rulers of the many Roman client kingdoms.
• Germanic tribes were similarly led by tribal kings, such as King Chrocus of the Alemanni, or King Ermanaric of the Goths, or King Maroboduus of the Marcomanni.

Given above, therefore, most of Europe were already governed by monarchies even before Rome fell. In fact, the establishment of the Roman Empire converted large swathes of Southern and Western Europe into monarchical rule.

Note that while much Italy and Greece had previously been oligarchies or democracies, most if not all originally had kings, such as the Roman Kingdom or Athenian Kingdom. Some even retained their monarchies until the Roman conquest, for instance Macedonia or Syracuse.

---

Your implicit question seems to be why Europe became governed by absolute rulers. That's a misunderstanding; monarchies are not necessarily absolutist. The kingdoms of Early Medieval Europe were mostly set up by Germanic peoples in the wake of Rome's fall, and consequently inherited the Germanic kingship of their earlier tribal governments.

While the specific varied, these kings primarily acted as military commanders and judges. Vestiges of these roles remained apparent today - all British criminal prosecutions are brought in the name of HM Elizabeth II, incidentally commander-in-chief of all British, Canadian and New Zealand forces.

In fact, up until the High Middle Ages, the power of kings were severely limited. Feudalism jealously guarded their power against royal overreach. The authority of early Kings of France were largely confined to Paris, while as late as 1215 the barons of England would force their king to agree to the Magna Carta. Scandinavian kingships retained their elective character into the Late Medieval Period, and the throne of Germany remained elective until the dissolution of the Holy Roman Empire.

All in all, absolutism did not really prevail in Europe until the Early Modern Period (even then, only briefly and to uncertain degrees).

Answer 2

1) Long before Rome fell it had abandoned Republicanism. After Diocletian and the Crisis of the Third Century the Emperors no longer felt any need to consult with the Senate. The Senate's role in government and in the legitimacy of the Empire was symbolic. This is the first flaw in the question - the transition between Republic and Monarchy occurred during the Roman Empire.

2) Greek Democracy fell to the Macedonians, although a more full discussion would include that (a) the Greeks abandoned democracy themselves more than once, and (b) Greek Democracy was actually an oligarchy - voting rights were invested in a small minority of the inhabitants.

3) Europe didn't pursue absolute monarchy for centuries. In the comments many others have noted that the governance model from the fall of Rome to the rise of absolute monarchy explored a variety of models. Most common, as I recall, was for those who wielded effective military power to select one of their number to exercise leadership, but that selection was limited and revocable.

4) Ultimately Monarchy wins out for a couple of reasons. Democracy and Republics suck at war. War requires effective command, and Democracy tends to provide a diffuse and inchoate command structure - Rome (and if I recall Greece) delegated to a dictator during a war. (I think one can argue that Democracy sucks at foreign policy in both peace and war.) Monarchy provides advantages for the organization and governance of societies of a specific size and technological level. hat tip to @bilbo_pingouin who suggested this revision Monarchy provides for a (relatively) stable succession, coherent governance, and strong effective states. Hat tip to @TheHonRose This changes somewhat in the modern age; @TheHonRose correctly points out that Churchill defeated Hitler; that democracies defeated empires in WWII. But OP is asking about a pre-modern time where war was fought & won with weapons is different from a modern time where war decided by industrial production. There is a fascinating essay there but (a) I'm not truly qualified to write it, and (b) it is non-responsive to OP's question. I'll stand with my thesis that during the pre-modern age, working with economies based on agriculture and land, that monarchy (and vassalage) is a more effective command and control institution. Rome was an aberration - Rome developed an educated class broad enough and deep enough to take advantage of a form of democracy, and an economic infrastructure that surpassed simple agriculture. (another interesting essay, but probably off topic).

Update - It occurs to me that I've neglected to address the underpinning of OP's question. Why monarchy over democracy? Fukyama's Origins of Political Order argues that democracy requires some relatively sophisticated institutions. (I'm abridging a book into a sentence; I'm aware of the injustice I do to his argument). Democracy is built on the notion that the citizens trust the state. In an era of poor communications, and unbelievable wealth gaps, it is difficult to assemble any meaningful demos. (Stop whining about today's 1%'ers; imagine life in Charlemagne's time, when 99% of the population legally could not travel from their home and would almost never speak to anyone outside their home village.) Greek democracy worked because it was a tiny oligarchy of citizens who knew one another. The same was true for the Roman Senate - a small coterie of families who knew one another, supported by tribes (who claimed kinship). Rome couldn't maintain the cohesion and degenerated to an absolutist monarchy, followed by a military dictatorship. There was no hope to build the kinds of institution and societal trust mechanisms that would enable democracy in societies with that kind of weak communications and cooperation.