By PAN PYLAS Associated Press

LONDON (AP) — The world economy faces a new threat. Instead of a banking collapse or too much debt, fears are growing that countries are using their currencies as an economic weapon.

History suggests that’s never a good thing.

If too many countries try to weaken their currencies for economic gain — sparking a ‘‘currency war’’ — that could stifle business confidence and investment, sow turmoil in financial markets and derail a fragile global economy.

As financial representatives from the world’s leading 20 industrial and developing nations gather for a meeting in Moscow this weekend, those concerns are being openly discussed.

‘‘All the members of G20 need to deliver on a commitment to move towards a market-determined exchange rate and refrain from competitive devaluation,’’ U.S. Treasury Undersecretary Lael Brainard warned Friday.

Why is everyone talking about currencies?

— Since the start of the financial crisis, central banks around the world have been trying to stimulate their economies by keeping interest rates extremely low. The goal is to encourage consumers and businesses to borrow and spend more. One way central banks drive down rates is to use their power to print money to buy up large quantities of bonds. But by boosting the amount of currency in circulation, there is a side effect: it can drive down the value of that currency relative to others.

As a country’s currency falls, its exports become cheaper, while those of its neighbors become relatively more expensive.