Country & City IDs

Hello,
In the MySQL format, IDs are specified explicitely. As localization data change over time, I would like to "store" city/country mapping to my records (visits).
However, I face a problem: I can reference a country and/or a city, by it's ID, but what happen if a country disappear or appear (for exemple Croatia appeared few years ago)?
Does each individual city/country keeps their ID ? Or I need to create a built-in mechanism to maintain a city/country database that will track changes over time ?
In short: does ID for a given country or city will be unique over time.
Thanks in advance.
In the MySQL format, IDs are specified explicitely. As localization data change over time, I would like to "store" city/country mapping to my records (visits).
However, I face a problem: I can reference a country and/or a city, by it's ID, but what happen if a country disappear or appear (for exemple Croatia appeared few years ago)?
Does each individual city/country keeps their ID ? Or I need to create a built-in mechanism to maintain a city/country database that will track changes over time ?
In short: does ID for a given country or city will be unique over time.
Thanks in advance.