evidence: we allow barbarians from the south to come and wipe our decadent arses, with the ultimate consequence that they will be the future of this geography, long after we've frittered ourselves into oblivion.
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Ah ha! You're starting to catch on. And we also have devised a delusion the the basic work that sustains this nation can be done elsewhere while our basic carefree concerns can be self-amusement, Britney Spears, and cults of personality.
Another pattern I find characteristic of decline is the evolution of a cult of inherited and/or soft leadership, whether it's degenerate Roman emperors, weak kings of France, or more cultivated weak useless families such as th Kennedys, Gores, incipiently the Clintons, and the Bushs.