The American-English expression dementia Americana denotes the (alleged) form of dementedness, leading to violence, that takes hold of a man who believes that his home has been invaded or that his family has been violated.

This expression was coined by Delphin Michael Delmas (1844-1928), the attorney who defended Harry Kendall Thaw (1871-1947), who, in 1907, was tried for the murder of the architect Stanford White (1853-1906); White had allegedly raped Thaw’s wife, Evelyn Nesbit (1884/85?-1967), when she was a chorus girl.

The following explanations are from “Dementia Americana”: Mark Twain, “Wapping Alice,” and the Harry K. Thaw Trial, by Susan Gillman, assistant professor of literature and American studies at the University of California, Santa Cruz, published in Critical Inquiry (The University of Chicago Press – Vol. 14, No. 2, Winter 1988):

Early in 1907 one of the twentieth century’s most notorious murder cases was making headlines in America and abroad with revelations of bizarre sex, violent jealousy, and hereditary insanity in the demimonde of New York’s high society. On the evening of 25 June 1906, following the opening performance of Mamzelle Champagne, the Pittsburgh millionaire Harry K. Thaw shot the well-known architect Stanford White in full view of the diners at the Madison Square Roof Garden—the building itself one of White’s most acclaimed designs. Thaw, charged with first-degree murder and on trial for his life, pleaded not guilty by reason of temporary insanity. The defense argued that Thaw’s long history of mental instability was aggravated by his wife Evelyn Nesbit Thaw’s story of how, as a sixteen-year-old virgin, she had been drugged and seduced by the much older Stanford White. Even though the alleged ruin of Thaw’s wife took place some (unspecified) time before her marriage and years before the murder, still the defense claimed that after Thaw proposed to Evelyn Nesbit in June 1903 in Paris (the first of two premarital and, it was noted, unchaperoned trips the couple took to Europe) and heard her story of seduction, his mental condition gradually deteriorated until three years later his delusions culminated in what he believed was an act of divine providence, the murder of his wife’s alleged seducer, to him a symbol of all depraved men who ravish innocent women.

In his final plea to the jury, on Tuesday 9^th April 1907, Delphin Michael Delmas invented the expression dementia Americana, as well as a national profile of symptoms, in order to give a general character to Thaw’s form of dementedness. The following transcript of this final plea was published in The Lima Times-Democrat (Lima, Ohio) of Tuesday 9^th April 1907:

“Ah, gentlemen,” said Mr. Delmas, turning to the alienists who testified for the prosecution, “if you desire a name for this species of insanity, let me suggest it—call it dementia Americana.
“That is the species of insanity which makes every American man believe his home to be sacred; that is the species of insanity which makes him believe the honor of his daughter is sacred; that is the species of insanity which makes him believe the honor of his wife is sacred; that is the species of insanity which makes him believe that whosoever invades his home, that whosoever stains the virtue of his threshold, has violated the highest of human laws and must appeal to the mercy of God.”

In his own final speech, William Travers Jerome (1859-1934), New York County District Attorney, was sarcastic of the expression dementia Americana. The following is from The Evening Star (Washington, District of Columbia) of Wednesday 10^th April 1907:

New York, April 10.—It was District Attorney Jerome’s turn in the Thaw case today. When court opened he began on behalf of the people the summing up of the prosecution’s case against Harry Thaw.
[…]
“Gentlemen of the jury,” said Mr. Jerome […].
“If you find that this defendant was insane when he killed Stanford White it is your duty to say so in your verdict. If you do not say so it is because you believe that this killing was justifiable. Justifiable does not mean ‘dementia Americana,’ it means self-defense; but when a man sits with his head in his hand and is deliberately shot with a pistol held so close to him that after the shooting the victim’s own brother-in-law did not recognize him, it can hardly be called self-defense east of the Mississippi river.
[…]
“You swore you would not inject any ideas of your own into your judgment, but take the law as it was laid down to you by the court. You swore you would accept only that form of insanity which deprives a man of the knowledge of the nature and quality of his act or that it is wrong—that is, against the current morality of the community. You did not swear to bring this ‘dementia Americana’ into the case.”
Each mention of “dementia Americana” was uttered by Mr. Jerome with a sarcastic inflection.
“Dementia Americana, men,” he said, “has no place in your verdict. You swore to take no higher law than the law of your state.
“Dementia Americana! What is this dementia Americana which waits and glares at its enemy for three years and then kills? It waits three long years and grows bitter and then strikes.
“Dementia Americana—that flaunts the woman for whom it kills through the capitals of Europe for two years as its mistress. Is that the higher law?
“No, gentlemen, the higher law does not hide itself under the hem of a woman’s skirt.
“Dementia Americana—is that the law which puts a woman up to tell of her shame—or misfortune, as the case may be—to all the world in the hope it will shield a worthless life from a people’s just demand?
“That is not the kind of law you swore to accept, and if you do it, men, you violate your oaths.”

The expression dementia Americana immediately became popular, and was applied to any form of insanity, or even to foolishness. These are three examples of this use:

1-: From “Regulating Ruin”, published in The Journal and Tribune (Knoxville, Tennessee) of Tuesday 26^th November 1907:

Senator John C. Spooner, who was in congress at the time the Sherman anti-trust law was passed and voted for the law, now says he made a mistake and his eyes have been opened. He declares “you cannot regulate that which you destroy.” The proposition is self-evident and will not be assailed. He seems to believe the Sherman anti-trust law attempts to regulate that which it destroys.
Using a term used by a celebrated California criminal lawyer who appeared in a murder case that was given national notoriety, at the time the Sherman law was passed there were symptoms of “dementia Americana,” afterwards it became epidemic. Demands so general were made that something had to be done, it is possible that the remedy has been too drastic, in some respects as deleterious as the disease.

2-: From Coyote Center Taken in by Solemn Looking Stranger, in the Tales of Hank Stokes series, by Elmer Rigdon, published in The Pittsburg [sic] Press (Pittsburgh, Pennsylvania) of Sunday 1^st December 1907:

“Well,” replied Sandy, “while you air discoursin’ you hed better hev a drink on the house.”
“Thet’s the p’int; we can’t.”
“What! None of you?”
“Nary a hidebound critter.”
“Mebbe you air only temporar’y off yer feed; or is this anuther case of Dementia Americana?”

3-: From the column Short Sport, published in The Akron Beacon Journal (Akron, Ohio) of Thursday 12^th December 1907:

Some writer, who is suffering with dementia Americana, says that Barney Dreyfuss is laying lines to acquire the St. Louis Nationals and make the Pirates a sort of subsidiary team. Pittsburg [sic] is a better base ball town than St. Louis ever was or will be.