Very interesting observation. Curious, what are some good examples of this in the past?
Prior to Nazi Germany, the Germans were relatively normal. In a couple years time they went stark raving mad and reversed most of what thy were as a people.
Roaring 20s, Weimar Germany.
You can certainly easily go back at least as far as Gibbons' The Decline and Fall of the Roman Empire. But the *Tulip Mania* of circa 1630 seems also to qualify, followed by the English Civil War of 1840, the *Bishops Wars* between Scotland and England of 1642-1651, the Catalan Revolt in Spain [1640-1659] and the Siege of Candia [modern Heraklion, Crete] was in which Ottoman forces besieged the Venetian-ruled city. Lasting from 1648 to 1669, or a total of 21 years, it was the longest siege in history.
More subtly, four decades prior to the American Revolution of circa 1776 and the French Revolution of 1789, came the publication of Montesquieu's Considérations sur les causes de la grandeur des Romains et de leur décadence (Considerations on the Causes of the Greatness of the Romans and their Decline.) Montesquieu was a French lawyer and political philosopher who lived during the Age of Enlightenment and gave us both the theory of separation of powers and the term despotism. The period also gave us the of England and Boston, and, in France, the Marquis De Sade, followed by the Franco-Prussian War.
Similarly, the reactions to the poetry of Charles Baudelaire, particularly Les Fleurs du Mal in 1857, Darwin's, The Origin of Species in 1859 and Uncle Tom's Cabin; or, Life Among the Lowly, by American author Harriet Beecher Stowe, published in 1852 helped lay the groundwork for the American Civil War in which about 2 % of the American population and around 10% of the male population died.
By the earliest days of the XX Century, social changes that preceded economic waves could also bring sudden changes in sometimes barely-stable political times, as in Mexico with the 1910 Mexican Revolution/ Mexican Civil War (Spanish: Revolución mexicana) or Mexican Civil War led by Francisco I. Madero against longtime autocrat Porfirio Díaz, and lasting for the better part of a decade until around 1920. Over time the revolution changed from a revolt against the established order to a multi-sided civil war, and included a few forays into the United States, notably the Pancho Villa-ordered raid on Columbus, New Mexico on March 9, 1916, and followed by [or including] the anti-Catholichttp://en.wikipedia.org/wiki/Cristero_War Christero War until around 1926.
The same period saw Europe set afire during the time of the Austro-Hungarian empire and the sudden death on 28 June 1914 of Archduke Franz Ferdinand heir presumptive to the Austro-Hungarian throne, and his wife, Sophie in Sarajevo at the hands of an Serbian Nationalist assassin. After that, it's pretty hard to separate the social/economic/political causes of such harbingers of conflict, save maybe one I've observed:
From about 1955, when I first started noticing such things, until the last six months or so, there seems to be one common if not necessarily widespread harbinger that things may soon become sporty. Popular music, or parts of it, slow down and become reflective/maudlin or wistful.