Prior to WWII, America was barely a third world country with a mostly agrarian economy that didn't need much money. It also largely supported its need for money from an export market for its abundant resources, which is why it remained on the gold standard for so long.
The other major event in government finance that occurred in 1913 was the institution of America's central bank, the Federal Reserve. It was the third attempt at such an entity, the previous two being opposed by the wealthy and their bankers who financed politicians that guaranteed to kill it.
At the time, there were over 150 state and bank supported currencies in the US and each had its own exchange rate against the dollar and gold. This presented an impossible situation for interstate trade made possible by coast to coast rail. A unified currency was critical to economic growth and to offer stability to the dollar.
The fastest way to gain acceptance of a currency in any economy is to impose a tax on as many of the people as possible and require it to be paid in the currency the central government can produce at will. This makes everyone unemployed in terms of that currency until they can satisfy their tax obligation. It also deploys real resources into the economy that are then available to the government to purchase as it needs.
To this day, there is no law against any other currency being used in the US. It was never needed because the tax worked so well. The country quickly adopted the official currency of the federal government because of its superior ability to control the value and the fact that it was (almost always) spending more than it required back in taxation. This was only legal under a gold standard when the country was at war, which probably accounts for why we've been continually at war for all but about a dozen years since.
As long as the people can feel secure in their government's ability to create the currency it taxes in they will be happy. This means funding public works and infrastructure while leaving enough in the private sector to allow the people to save some as a store of value from commerce with their government.
While it was widely opposed by the people who didn't fully understand money, the move to a fiat currency (domestically in '34 and internationally in '71) allowed the government much more latitude in its budgeting and its ability to produce Treasury vehicles for investors. In fact, the availability of currency to the federal government to spend in the private sector became infinite, as was placed into record by a New York Fed Chairman in '45 in a paper titled "Taxing For Revenue Is Obsolete".
His name was Beardsley Ruml, and he was instrumental in formulating New Deal policies along with Eugene Debs in FDR's administration. He simply made the logical assumption that there is no "infinity+1" in math that would offer government a greater ability to create currency due to tax collections or bond issues.
While the wealthy should have been borderline orgasmic over such a revelation, they also saw the eventuality of a government creating too much security for labor and driving wages radically higher. And, of course, those who have the gold make the rules. They knew they could always heavily influence tax policy by simply buying a few politicians, so they have yet to acknowledge the value of the fiat currency in spite of receiving the lion's share of its advantages.
