In the early 20th century, Argentina and Australia were about equally rich-both European settler societies founded on expropriation of indigenous land, with economies dominated by export-oriented primary industries (agriculture and mining). But after that, they diverged-Australia’s economy just went up and up and up, Argentina’s went up and down and sideways. Why?

I think this article gets it wrong. Yes, Argentina owed lots of money to foreign bankers - but at some points in its history, Australia has too, and that debt became a burden (the 1932 NSW constitutional crisis in which the Governor dismissed Premier Jack Lang because he proposed not to repay the banks).

I think a major factor was Australia’s much greater political stability, which in turn could be due to a different political system. Many political scientists believe that a British-style parliamentary system [0] leads to greater political stability than the presidential system found in the US and most of Latin America. Leaders in parliamentary systems are forced to lead collegially, which makes the emergence of strongmen with personality cults (whether Peron or Trump) much less likely. I think the US is maybe somewhat of an exception-it has got so many other advantages, they make up for its deficient political system-much of Latin America, Argentina included, has never been so lucky.

[0] which doesn’t require a constitutional monarchy, you can have a figurehead President with little real power instead, like Ireland does