It is the constant complaint of older people that younger people have no manners. This is not a modern complaint, either--the Romans cursed the manners of their children, and complaints about how the young don't know how to behave are a constant in literature. But clearly, the decline in manners cannot be continuous throughout history or else we would have no manners at all by now and social life would have collapsed. So there has to have been a fluctuation, a waxing and waning throughout history, and clearly some societies pay more attention to manners than others do. Americans have always been famous for bad manners since the beginnings of the Republic. Mrs. Trollope and Charles Dickens both commented on this during their American sojourns, although Oscar Wilde observed that the best manners he ever encountered were among the silver miners of Colorado. He may have been being facetious, but maybe not. Manners, in the sense of not wishing to give offense, are typically punctilious in societies where men are armed and ready to use arms to revenge offense. Examples include the European gentry, the Japanese samurai, and the inhabitants of the Southern United States. My sense is that actually Americans have comparatively good manners, at the extremes of social interaction. The British House of Commons is a place of appalling rudeness compared to the U.S. Senate. Within a particular social context, the risk of paying with life or limb seems to put a capper on untrammeled rudeness.
Outside that context--the society of gentles, let us say, or a familial or hierarchical structure--manners may vanish entirely and people can behave like brutes. We are all familiar with societies in which the home or shop is a place of wonderful manners, while out in the street it's dog eat dog. We should also not confuse bad manners with misunderstanding social mores. It seems to me that this is the origin of the reputation of Americans as boors. A famous example: in the saloon, Americans used to (and perhaps still do in certain locales) place a bill on the bar when ordering a drink and let the bartender take the price of each drink ordered out of the ten or twenty, leaving the change, until nothing remained or the customer left, leaving a tip. When US servicemen tried this in British pubs during the war it was accounted grossly insulting. Bad manners, G.I's!
It is the case, however, that cultural sensitivity is not America's strong suit. That we are made of a mix of cultures seems, oddly enough, to work against cultural sensitivity abroad. At home we seem to be better than most at living and letting live. When we kill (at least recently) it's personal and not in mobs bent on massacring across ethnicities; although we do kill personally more than any other rich nation. This may account for the famously good manners apparent in the most violent sections of the nation.
At bottom, manners are ways for people (especially strangers) to interact without causing animosity, distress or hurt feelings, and this requires a certain dissimulation. You say thanks for the lovely gift even when you hate it, you finish the awful meal with a smile, you ask for the butter instead of snatching it, and so on. Pushed too far, or course, dissimulation can produce a stifling, rigid, social order. Polite dissimulation can morph into hypocrisy, and enough hypocrisy presages the doom of a civilization, the familiar examples being ancient Rome, the imperial realms of Europe, and the late USSR. But from time to time, dissimulation goes out of fashion. Frankness and self-expression become the prized values, hypocrisy the only sin, and manners are a casualty of such an age.
We live in such an age. As the classes become more isolated in reality, we deny the existence of any demand for deference--the clerk is your best pal and calls you by your first name. Ceremony is drowned, formal relationship is abandoned, casual Fridays encroach on the rest of the week, the untrammeled child becomes the social ideal, and actual children are utterly uncontrolled. But people can't live like this forever--it's literally inhuman--and the pendulum has begun to swing back. There is a reason why so many people are reading Jane Austen and watching Downton Abbey. Men are buying more suits, and the bookstores are full of books of rules. The cooking craze, with people sitting down for elaborate multi-course meals, is part of this trend, as are those books lambasting American child-rearing practices.
I'm going on about this because my novel is largely about two of the great historical transformations in manners, the one that occurred at the time of the French revolution, when the manners of the ancien regime gave way to the manners of the revolutionary-Romantic era, and the one where that in turn gave way to the manners of the Victorians. The central relationship in the novel is between a man who cam of age in the 1780s and his grandson, a product of the 1840s. Those who lived through the manners apocalypse of the 1960s will undoubtedly feel right at home.