Neutrino Cannon posted a link to a comment dialogue between Clio and Vladimir, on monarchy, with Vladimir taking the reactionary position.
The discussion includes the question: Why did Europe's monarchies fall?
Neither participant gives any attention to a theory I quite like, which is that the devil did it.
When there was only one religion, loyalty to the monarch was an moral absolute.
After the reformation, religious loyalty took a higher place than any other.
Edward, Mary, Elizabeth and James managed to navigate the new waters, though not without difficulty or incident. Charles ran aground, and while the Commonwealth failed and was rejected, enough of the theory it established survived to poison history ever since.
In France, anti-clericalism became a more important force than protestantism, but undermined monarchy also. That's secondary though: I think it's easy to underestimate the influence of the English revolutions of 1688 and 1776 on the French. It's true that England never got on with the revolutionary French regime, but isn't that often the way of things when a democracy thoughtlessly stirs up revolution in other countries? Writers in England and America were writing retrospective justifications for their seizures of power, and those were used by the Jacobins and later the 19th century European revolutionaries. Most of Europe was still monarchical until WWI, and Woodrow Wilson wiped the rest out in 1919.
There really was a total change in the dominant political ideology of Christendom, from Divine Providence to Nationalism and the Rights of Man. I personally don't actually believe "the Devil did it", but if I had to pick one point to represent Satanic interference in history, that would be it. Marx and Hitler were just products of history, aftershocks of that cataclysm.
As the power of religion to justify kingship waned, there were attempts to put monarchical centralism on a firmer theoretical footing than Divine Providence. Perhaps Hobbes is the first Neoreactionary. But the Whigs won out.
Update: don't miss Devin Finbarr's contribution: the unexpected richness of North America gave defeated radicals a springboard to return with power