So from my "Personal opt-outs for integration (UK and Europe and elsewhere)...." thread in Chat I discovered (and posted) the interesting tidbit of info which suggest that the United States itself is not an optimal currency area (i.e. "a geographical region in which it would maximize economic efficiency to have the entire region share a single currency").
In fact when Michael Kouparitsas did a study on it and published the results in a 2001 paper he found that out of the eight regions into which the Bureau of Economic Analysis (BEA) divides the USA about five of them (New England, the Mideast, Great Lakes, Rocky Mountains and Far West) were core regions "that have similar sources of disturbances and responses to disturbance" and the remaining three regions (Southwest, Southeast and Plains) were non-core regions that differed greatly from the core regions. I mapped it out in that thread of mine in chat and I've linked the map image below. Basically it would seem that only the areas in green on the map constitute an optimal currency area (I've coloured the other 3 regions separately since they don't necessarily constitute an optimal currency area combined. Note that the BEA's regional boundaries are coloured red).
So the challenge is to get these three regions (basically the Greater South and the Plains states) to be given their own subnational currency or currencies by the present day. The POD could be any time, but since the optimal currency area theory hadn't arisen until the 1950s/1960s I can't imagine any POD being derived from an earlier attempt at optimal currency area study of the United States allowing for subnational currencies before that time. Of course if it is easier a POD could be done from before 1900 and it would just so happen that a subnational currency or currencies would only remain in use in those areas whilst the rest used the standard United States dollar. If US territories also end up with their own currencies it would be a bonus.
In fact when Michael Kouparitsas did a study on it and published the results in a 2001 paper he found that out of the eight regions into which the Bureau of Economic Analysis (BEA) divides the USA about five of them (New England, the Mideast, Great Lakes, Rocky Mountains and Far West) were core regions "that have similar sources of disturbances and responses to disturbance" and the remaining three regions (Southwest, Southeast and Plains) were non-core regions that differed greatly from the core regions. I mapped it out in that thread of mine in chat and I've linked the map image below. Basically it would seem that only the areas in green on the map constitute an optimal currency area (I've coloured the other 3 regions separately since they don't necessarily constitute an optimal currency area combined. Note that the BEA's regional boundaries are coloured red).
So the challenge is to get these three regions (basically the Greater South and the Plains states) to be given their own subnational currency or currencies by the present day. The POD could be any time, but since the optimal currency area theory hadn't arisen until the 1950s/1960s I can't imagine any POD being derived from an earlier attempt at optimal currency area study of the United States allowing for subnational currencies before that time. Of course if it is easier a POD could be done from before 1900 and it would just so happen that a subnational currency or currencies would only remain in use in those areas whilst the rest used the standard United States dollar. If US territories also end up with their own currencies it would be a bonus.