SWIFT, the financial messaging network that Western-led banking runs on.
It's the shared rail that lets banks around the world send each other payment instructions.
Because it's Western-controlled, it was used to punish Russia with sanctions — and that very act of using it as a weapon pushed other countries to build alternatives, with a new system called mBridge threatening to make SWIFT just one option instead of the only one.
If the world stops needing SWIFT, the West loses a major point of financial control over everyone else.