base - preselect one field by another

I am trying to make a database with some basic geographical data in it (city, region, country.
A region tends to only be in one country, so I would like to have the country preselected as soon as the region is selected.

I did get this working, were it not that I then end up with as many country-entries as there are regions for that country in the database.

I tried to make two separate tables
tbl_region
ID Int
region Text (varchar)
country Int

tbl_country
ID Int
country Text (varchar)

I also have a main table with other data in it, which has an Integer for Region.

Every time I try to get these fields into a form, Base crashes.