Dollar bills under the circa pre-Nixon gold standard were IOU for gold, there was no need to have enough gold to cover them as it was a fractional reserve.

So why gold? Why not buildings or factories or railroads or ports?

Not going to be answered in a one liner but the short answer is historically it had about the highest density of value that was relatively easy transport, divide, and the inflationary properties though highly imperfect were less susceptible than that of factories or railroads. Humanity came to it empirically.

Many people have suggested alternatives such as units of energy or baskets of goods but at the end of the day there is no perfect unit, dollars being backed by essentially largely threat of imprisonment if you don't pay your taxes and scarcity of how many the government decides to 'print' is yet another arbitrary choice of backing.

How do you ship fixed infrastructure to another country when they want to redeem their USD?

You don't. You give them a title to the infrastructure. Exchange paper for paper. Pretty neat right?

Developed real estate titles are notoriously one of the least fungible assets in existence.

Relatively uniform rural undeveloped farmland titles might work but I doubt it would get the same historical inertia since gold outlasts governments more reliably than land titles.

That's a problem for any foreign holder of USD who wants to redeem it. So far they've been ok with it.

(I didn't mean the government hands out land titles. The holder of USD uses it to buy assets in the country)

I've re-read your statement several times and I'm still not quite getting it. If your point is that railroads or factories are as valid a basis as 'can be used to bail someone out of IRS agents with machine guns shooting their dogs and putting them in a little cage' than I agree with you.

Although it brings me back to, you can see how maybe it was simpler historically for people to just settle in a fungible, transportable, easily dividable hard asset that had essentially as good inflationary properties as anything else they could find.

I can see how it was simpler historically, when factories and buildings and patents weren't worth all that much.

I've tried this point before but it always fails because the argument is, if I may contrive a straw man, that the government can simply machine gun everyone at the exits, take all the gold reserves, and cancel the notes. Therefore any government enforced asset is basically as good as gold in this regard because the government can and has (circa great depression) simply cancelled the trustless or bearer properties of gold.

Although you're right that this is historically a large element of gold exists it won't be accepted as reasoning, and it's not worth bothering on places like HN.

I think the hope that international bearers would have is that thet can get their gold out when the future is looking risky, but before a breakdown in trust comes to that level. Once the revolution actually happens, Fort Knox is in enemy hands.

> A claim to infrastructure that can simply be nationalized

If your currency is in such high demand that people still accept it, even knowing this, that's a feature not a bug. You hopefully never have to use but it remains as a nuclear option.