After World War III, economy on Earth suffered from three major factors that brought worldwide finance transactions to their knees.
The first factor was war damage to the infrastructure. War had devastated Asia, Northern Africa and huge parts of America and Europe. A total naval war had been fought especially on the Pacific Ocean and whole merchant fleets had been eradicated. Nuclear weapons had rendered agricultural areas for cultivation in Russia and Asia useless. The old nation states had to add huge war debts to their stressed balances.
Additionally, national economies basically had ceased to exist if nations had joined one of the bigger unions. Those unions (e.g. the Southern African Alliance) had been formed to fight the augment aggressors and their constitutions were somewhat written in a fashion that reflected their initial purpose. Especially African and South-Asian supranational states had used the opportunity to simply cancel any debts still owed to other states.
A third factor had only been accelerated by the World War: Natural resources were on an all-time low. Extractable fossil fuels had been depleted almost entirely and the only industrialized areas capable of producing rare earths were within the territory of the former Eastern Coalition.
As a result of these problems, international trade became less important than regional, bilateral treaties. The international financial sector effectively had dissolved by 2064. The International Monetary Fund had been inert for years, there were no reliable methods of transferring money by computers and the internet had been fractured into regional networks.
Modern mass migrations occurred especially in Northern America, the area of the former Eastern Coalition and Southern Europe as many people moved away from major cities and nearer to production facilities, establishing de-facto independent local sufficiency communities.