One way to think about it is what if we’d done it the other way around? If we’d had AI first at 20% GDP investment levels, would the subsequent railroad boom have been an order of magnitude smaller at 2% GDP?

For me, that’s enough of a thought experiment — as implausible as it might be to have AI in 1901 — to be skeptical that the difference is simply that the first tech step-change was a pre-war uplift to build the post-war US success story, and the latter builds on it.