Is there any quick guide/reference to list all the countries and its states/provinces?
Like when I click US, it will list: Alabama, alaska etc
pycountry is the most complete free reference I was ever able to find:
pycountry provides the ISO databases for the standards:
639 Languages
3166 Countries
3166-2 Subdivisions of countries
4217 Currencies
15924 Scripts
The databases are imported from Debian's pkg-isocodes, packaged into pycountry and made accessible through a Python API.
Translation files for the various strings are included as well.