The US monetary union has undergone four distinct phases of development. From the early colonial period through the Revolution and Confederation, the unit of account differed in each region of British North America. Soon after the Constitution went into effect in 1789, the country shared a single specie-based unit of account and standard of deferred payment, but exchange media were numerous. After the Civil War, the trend was towards the use of fewer media of exchange. Over the course of the twentieth century, the current system, characterised by a common medium of exchange denominated in a single unit of account divorced from specie, evolved.