> There's long been a hope that integration into the wider economy prevents war - the idea being that countries that trade deeply won't fight each other.

There was a guy by the name of Norman Angell, who wrote a book called "The Great Illusion" about that exact thing. The premise, to quote Wikipedia, was that "the economic cost of war was so great that no one could possibly hope to gain by starting a war the consequences of which would be so disastrous", on the basis of considerable economic interdependence of major powers.

The book was published in 1909.