The US dollar became the de-facto international currency, because it was "good as gold." If you had a US $20 bill, you could turn it in for a 22-karat gold double eagle. The slip of paper was simply the title to the gold. So the "international currency" wasn't actually the US dollar, it was gold, and gold still is today.
The fact that the US dollar still clings to the "international currency" designation even though it was detached from gold long ago is just an indication of the overwhelming inertia of the international financial system.
But gold cannot lie. Anyone can test it and determine its weight and purity. This fact is why FDR criminalized the possession of gold coin in 1933, as he went about ripping the heart out of the US dollar and replacing it with a web of lies spun by the Federal Reserve Bank and the US Treasury. The gleam of legal gold would have outshone the tarnished brass with which he replaced it, and he couldn't have that.
As a result the dollar has been in more-or-less free-fall ever since then as you can see from any graph, steadily destroying the hard-won savings of hundreds of millions of people, channeling it into the insatiable maw of big government. Unless you use a logarithmic scale, the line goes nearly straight down by 1990 or so.
If you have gold, as Ron Paul was saying here, you don't need the hollow assurances of corrupt, self-serving governments in order to trade with anyone, anywhere in the world. You have gold, and that's all you need.