Baldilocks cites a friend who brings up the “you’re another!” defense against criticism of Islam. Juliette does a pretty good job of expressing what I might call the conventional response to it, but hits only tangentially something her friend misses entirely: societies, like anything else, change over time according to the pressures of their environment — more precisely, according to their responses to the pressures of their environment.
When the Romans first came to Europe as conquerers, Europeans were as tribal as any group of societies on Earth. Clans and nations had begun to emerge — that’s the whole point of Omnia Gallia in tres partes divisa est — but Celtic tribes fought with one another, Picts had little organization above the tribal level, and the German tribes, in particular, were constantly engaged in bloody internecine warfare. This made it relatively easy for Julius and his legions to overrun the place, despite being far away from home base with a supply line that crossed some pretty impressive mountains and primitive transport infrastructure. The legions could attack and subdue individual tribes without much interference from their neighbors, because the neighbors were bitter rivals of the tribe being attacked and wouldn’t come help. The whole process was a definitional example of defeat in detail, and it didn’t even slow down, much less come to a halt, until German leaders appeared who realized what was going on and were mean enough to unite the tribes against a common enemy; the pre-eminent one of those leaders was also the one who gave his name to the whole people.
(Note 19 Sept: I have been informed that the struck-out clause is incorrect, and after only a little research I find that that’s true. “Why” would be an essay as long as this one, but the point is not central to my thesis, so the best thing to do is simply strike the offending matter.)
Romans really believed in their system, and as they conquered areas of Europe they made it a point to destroy tribal governance and introduce Roman administrative procedures. That produced some extremely strong polities as regards both military and societal strength, and tribes seeing themselves as next on the list observed that and introduced modified versions of Roman concepts, becoming more cohesive thereby. That tendency, combined with increasing corruption of the Roman system at home, was the Romans’ ultimate undoing. Both the polities they created and the mirror images produced by people under attack became strong enough, first to stand alone, then to resist what is now called imperialism, and finally to abate the nuisance by striking at its source.
The remnants of Roman administrative procedures remained in place once the Romans themselves were sent packing, modified by the equally revenant tribal structures they supplanted. That mixture produced the familiar European organizational structure: local barons controlling relatively small areas or groups that echoed the tribal system without being based on blood relationships, dukes controlling what were structurally clans that equally lacked strong blood ties, and kings at the head of nations that were, in fact, distinct from one another according to blood relationships, much attenuated. It worked because it was flexible at all levels — a barony (tribe) challenged by another could resist on that level, and get support from higher levels when it was needed for a stronger threat; a king could call on the whole nation to support defending against, or issuing, a threat based on the full strength available.
Tribal rivalries had not been eliminated. They had only been redirected into a new organizational structure that turned out to be fearsomely effective — and Europeans, especially Western Europeans, employed that structure to embark on two millenia of increasingly bloody, vicious, and expensive warfare, which reached its apotheosis in World War II. The really decisive conflict in that ongoing cycle of violence, though, was the Thirty Years’ War, which destroyed the Church as a political force.
Romans were polytheists; they also had (at least during the Republican period) an attitude toward governing and power that looks very odd to us today. Anybody who actually had significant power over any part of the society either became part of the Government or got whacked, hard — Senators were not so much elected as co-opted, on the ground that anybody rich enough to affect the Republic as a whole would damned well play well with the others, or else. Priests were clearly power-brokers because of their followings of believers in their particular gods, but they didn’t fit within the wealth-based Senatorial structure, and there was a secondary problem: co-ordinating feast days, parades, and other expressions of priestly power based on multitudes of followers. The solution was the indifferent church.
It was “indifferent” because it didn’t matter what god or gods the particular priesthood served; they would, like people who were rich enough to be powerful, accommodate themselves to the New Order or find themselves in deep trouble. It was a “church” because it had to do with religion, and the pragmatic Romans saw no need to invent a euphemism; but it was, at root, an administrative measure — in modern American terms, call it the Department of Religion. The chief priest of a major god became an episkopos (later bishop) administering a god-concession (diocese; think franchise in modern terms). To head it up the Romans reached for one of their unifying myths, the bridges across the Tiber and other streams that connected the otherwise-disconnected bits of their capital: the new post was chief bridge-builder (to the gods) — the pontifex maximus, chosen by the bishops in conscious imitation of Senatorial procedure, with an overlay of mysteriousness that could be presented as magical or god-influenced.
The indifferent (catholic) church existed perpendicular to the other lines of power and influence within Rome, and continued to exist as Empire succeeded Republic, became a power in the known world, and eventually split into Eastern and Western units. Like any other source of power, it got involved in power struggles and rivalries, but the structure remained intact. When the Emperor Constantine “took the Empire Christian”, he decreed the takeover of the administrative structure as it existed, and had plenty of thugs to make that ukase effective. By then the normal or traditional infrastructure of Roman administration had become corrupt and often ineffective, and by unifying the church under direct Imperial administration Constantine could both extend Imperial power to the remote provinces and discipline the governors and consuls whose power devolved from the Imperium along the original lines.
When the Empire collapsed under the combined weights of internal corruption and external forces, the Roman Church (now deserving its capital letters) regarded itself as the remaining unifying force of the Empire, complete with its duties to supervise lower-level administrative units to keep them in line with the aims of central authority. The Empire became, in the eyes of the Church, Christendom — the Domain of Christ — with themselves as administrators. Unfortunately it lacked the firm thumb of Imperial authority to keep itself in line; it quickly became corrupt, bribed and intimidated by the rulers of the polities that sprung up in the wake of the Empire’s dissolution, and divided by power-seekers within its own structure who employed different interpretations of Scripture (heresies) to build bases from which they could seize power.
In order to preserve its power and keep its cohesion, the Church ruthlessly played kings and princes off against one another and against outsiders, fostering violent petty rivalries that kept Europe splintered into warring factions; the Crusades can be understood, from that point of view, as an attempt by the Church to cement its position as judge and ruler of princes in the face of the centrifugal forces they otherwise fostered to keep the individual rulers subordinate to their influence. Europe became a battleground in which technological advances were mainly employed as better ways to kill people, and “peace” became “an ideal we deduce from the fact that there have been intervals between wars.” This was not entirely a negative. The military technology and theory thus fostered, combined with the remnant unifying force of the “Christendom” concept, enabled Europeans to coalesce into an effective resistance to the imperialism of the Caliphate, once their noses had been rubbed in it hard enough.
In the course of that effort the Church became so corrupt, so nakedly power- and wealth-oriented, that it ultimately lost its effectiveness as a unifying force against the splintering it, itself, had fostered. Martin Luther challenged it on spiritual and theological grounds; that challenge ultimately resulted in the Thirty Years’ War, the main effect of which was to eliminate the temporal, political power of the church as arbiter among rulers. But although the Thirty Years’ War was decisive, it did not stand by itself; it was, rather, the ultimate result of centuries of wars and political influence peddling.
Over the course of that period, Europeans, especially Western Europeans, killed off a lot of genuinely stupid people, raising the average intelligence level. At the same time, Europeans compiled a pair of extremely thick books, neither of which has actually been published, but which exist all the same: One entitled Ways to Do It, largely but not entirely devoted to military theory and technology, and another, much fatter tome, the spine of which is emblazoned in big gold letters Things That Don’t Work. Both volumes are compendia rather than expositions of a unified thesis, so they contain much that is repetitive, contradictory, and confusing; they are, nevertheless, the fundamental reference works that have enabled Western civilization to become dominant, and the founding principles of the United States are compiled excerpts from those books.
Several chapters, and a voluminous appendix of references and cross-references, in Things That Don’t Work are devoted to “theocracy”, “holy war”, and related subjects. Western civilization has, indeed, killed a lot of people, supported a great deal of tyranny and oppression, and smashed a lot of wealth in the name of Christ the Redeemer and His Holy Word. That isn’t going to happen any more, because we know in detail what the results are, and those results aren’t pretty. We’ve cropped that pasture as far as our tether will reach and as short as our teeth are long, and at long last have noticed the barren desolation it produces. There are, and always will be, kooks and nutcases who want to start it up again; the intelligent ones can be given a copy of Things That Don’t Work with the proper passages highlighted, and they will help stifle the stupid ones who will never figure it out. Theocracy ain’t gonna happen. We know how it works — or, rather, how it doesn’t.
There is an important exception to that, but this essay is long enough; leave it for another day.
 The sequence is individual, family, tribe, sept, clan, nation. Not all societies go through all the steps — the Scots, for instance, never really formed a nation until well after the Roman period. (This is at least partially because the Romans were ‘way out at the end of their lines of support, and the Scots’ clan alliances were sufficient to resist the relatively weak challenge.) Very few societies have ever fully developed the sept structure.
 The Latin word “imperator”, from which “Emperor” and “imperialism” are derived, was an accolade awarded by Roman troops — “this person is smart enough, mean enough, and well enough organized to give us orders we respect.”
 With, of course, help, however unintended, from forces, mostly from northwest Asia, that had developed clan structures into much stronger and more numerous versions without actually modifying the basic procedures.
 Yes, I know, ridiculously simplified. It’s an essay on a blog, not a thick book.
 And still have not been. It is ridiculously easy, even today, to find Europeans who are firmly convinced that the genetically-identical people on the other side of the river or hill are subhumans fit only for extermination. For various reasons this effect is weakest in England, which is where the English got the strength to form Great Britain and turn a good bit of the world map red.
 Imagine a future in which the United States has separated into squabbling smaller polities, but the Environmental Protection Agency is still doing business from the same building and working toward the same goals. Not quite the same, but a strong parallel.