Logic behind registration country codes

Anyone on here knows more about the history behind the country part of aircraft registration
Dutch: Was 'H' for Holland, changed to 'PH', 'PJ' and 'PK'
UK: 'G' for Great Britain
Iran: 'EP' Empire of Perisa.
China: 'B' for Beijing
But why did the US get the 'N', and where do all those 'V*' codes come from that are often used by ex-british colonies
Dutch: Was 'H' for Holland, changed to 'PH', 'PJ' and 'PK'
UK: 'G' for Great Britain
Iran: 'EP' Empire of Perisa.
China: 'B' for Beijing
But why did the US get the 'N', and where do all those 'V*' codes come from that are often used by ex-british colonies