The Days They Changed the Gauge

US North and South had different rail track gauges. They fixed it pretty much all at once.

I’m glad I ran across this after the update, as this interesting observation was added (quoting from one of the links)

As things turned out, having different gauges was advantageous to the South, since the North could not easily use railroad to move its troops to battle in southern territory during the Civil War. Noting this example, the Finns were careful to ensure that their railroads used a gauge different from the Russian railroads! The rest of Europe adopted a standard gauge, which made things easy for Hitler during World War II: a significant fraction of German troop movements in Europe were accomplished by rail.

Also the note about how the standard gauge was adopted after secession, so there was no opposition from the South. Adoption of standards is usually contains a large dose of politics. If the dissenters aren’t in the room, consensus is easier.