“History is philosophy teaching by example, and also warning; its two eyes are geography and chronology.”

On the Study and Use of History, letter 2; in fact this relates to a third-century CE treatise on rhetoric, wrongly attributed to Dionysius of Halicarnassus, which says (xi. 2): "The contact with manners then is education; and this Thucydides appears to assert when he says history is philosophy learned from examples". The line is not found in Thucydides.

"War Is God's Way of Teaching Us Geography" https://quoteinvestigator.com/2014/05/19/geography/ at Quote Investigator
"The comment 'War is God's way of teaching Americans geography,' is continually attributed to Ambrose Bierce. Biographer David E. Schultz, who has nearly all of Bierce's writing entered on his computer, cannot find this acerbic remark within that database." Ralph Keyes, The Quote Verifier (2007), p. 240
Misattributed

History of Mathematics (1923) Vol.1

L. Randall Wray, The Credit Money, State Money, and Endogenous Money Approaches: A Survey and Attempted Integration. (2005)

Source: Man, the State, and War (1959), Chapter IV, The Second Image, p. 107

Variant: If you can't be a good example, you'll just have to be a horrible warning."
-Gwen Goodnight
Source: Faking It

To the twenty-fifth-anniversary meeting of the Massachusetts Anti-Slavery Society (1857)
1850s