The dollar is what the world uses for transactions. The more other countries use different currencies for trade among themselves, the less demand for dollars.
Us currency is one of the safest and most secure in the world. International investors gravitate to such currencies when investing. When interest rates in such countries increase the demand does for that currency does as well. You can’t “buy” a CD, Treasury note, etc. or goods and services without converting the foreign currency into US dollars first. This is how exchange rates are determined. If you are in Europe and buy my US product I want to be paid in dollars. International currency transactions of these sorts on a daily basis dwarf the level of volume on Dow Jones by a large margin.