LONDON, July 8 — What makes a currency the world’s default? It is a question that sounds abstract but has very concrete answers. The US dollar holds that position today, and the mechanics of how it works are surprisingly straightforward.
A reserve currency, by definition, is one that central banks and major financial institutions hold as part of their foreign exchange reserves. The dollar performs three distinct jobs in the global economy.
It acts as a medium of exchange for international trade, a unit of account for pricing commodities such as oil and gold, and a store of value for central bank reserves. The scale of the dollar’s dominance is striking. According to the Bank for International Settlements (BIS), as of 2023 the dollar is involved in about 88 percent of all foreign exchange transactions.
That figure alone explains why shifts in US monetary policy matter far beyond America’s borders.
How the system works
Many countries peg their own currencies to the dollar. China, for instance, manages the renminbi against a basket of currencies but gives heavy weight to the dollar. This creates a direct transmission line: when the Federal Reserve adjusts interest rates, the effects travel through these pegs and managed floats into economies around the world.
The dollar is also the primary currency for international debt issuance. About 60 percent of global debt securities are denominated in dollars.
That means borrowers from Buenos Aires to Bangkok must earn or borrow dollars to service their debts, tying their financial stability to the health of the US economy and the Fed’s policy choices. Central banks hold their dollar reserves primarily in the form of US Treasury bonds. These are considered safe assets — a status that has held through financial crises, wars, and pandemics.
The demand for Treasuries from foreign central banks helps keep US borrowing costs lower than they would otherwise be.
Global ripple effects
The Federal Reserve’s monetary policy decisions do not stop at the water’s edge. When the Fed raises rates, it can strengthen the dollar, making dollar-denominated debt more expensive for foreign borrowers. When it cuts rates, capital often flows into emerging markets seeking higher yields.
These are not theoretical possibilities; they are observed patterns built into the architecture of the global financial system. What researchers have found is that this system creates a kind of gravitational pull.
Countries that want to trade internationally, borrow in capital markets, or maintain stable exchange rates find themselves drawn into the dollar orbit. The alternative — building a parallel system — would require enormous coordination and trust among nations that do not always see eye to eye. For now, the dollar’s role as the world’s reserve currency rests on a combination of deep financial markets, the rule of law, and a track record of relative stability.
Whether that position erodes over time depends on factors that no central bank controls alone: geopolitical shifts, technological change, and the decisions of the billions of people who use money every day without thinking about what props it up.
