1873 is one of those constant financial bubbles where overoptimistic speculators and investors wildly overestimate when a new industry will be profitable, rogues use that to build personal empires, and financiers cheat everyone in sight.
In 1873 it was building the western railroads (Richard White's new economic history of the Western Railroads' chicanery, "Railroaded" is highly recommended) and along with their construction there was vast real estate speculation assuming the new towns would be instantly viable and land prices would go up and up (as opposed to taking decades to develop which many didn't and to develop sufficient traffic/loads to make the railroads viable.)
It's a replay of the English South Seas Bubble and French Mississippian Bubble both assuming remote territories would in a year or two turn into thriving cities/trade empires...we did it most recently in the dot.com and fiber optic network bust of 1999-2001 or the housing bubble just now.
Part of the reason it's a worldwide hit is so much of European capital was funding the Western railroads and related development (the Northern Pacific Railroad for example drew mostly on German and Serbian investors) who lost that investment completely in most cases. Whenever a bubble is wiping out painfully and long accumulated investment capital and debt capacity for no productive purpose (but enriching scoundrels), it takes time to recover and many never do. Investing in the development of new territories, overseas colonies, new technologies, etc. always pays off far slower than anticipated with a huge amount of capital completely destroyed along the way, in the same way gamblers brag about their wins and downplay their comparative losses.
The POD would probably be Jay Cooke, the Philadelphia bond financier, dies about the end of the Civil War (which he'd been key in helping the Union finance with creative bond issues) along with a couple of other key fools, different people/firms win the contracts to build the western railroads with much more effective oversight/far less Congressional corruption, and the development out West is tied more to economic realities (so it works better and earlier) than deeply ignorant speculation. It's not even easy to say, hellish to do as you'd need many simultaneous POD's for the thread.
More like herding cats than a single decision going the other way.