Hello @Jacques Cormier
According to help, the only reason could be the country is not enabled for usage or it is enabled but at the same time blocked for usage field is set to TRUE. If both used in application and blocked for usage is enabled, you will not get the country.
See the help for country field.
Select the appropriate country from the drop down list. The country you choose has no practical meaning in the Enterprise component. It is only dependent on how other installed modules utilize it. The IFS/Accounting Rules component is one example. Some posting types can be governed depending on the choice of country. The available countries are those marked as Used in Application in the ISO Code Usage/Country tab. Contact your System Administrator if a country you want to use is not visible. It is possible to change the country after saving.