By creating a Country Custom Field you would be able to collect the country in which your subscriber resides in through your Subscription Form.
Please note that the custom field is global and will be available across all lists in your account.
To create a Country Custom Field, follow the steps below :
Click on "Custom Fields"
Click on "Presets"
3.1 Click on the "Preset" dropdown box and select "Country"
3.2 Click "Create Custom Field"
Your Country custom field has been created, now when you create your subscription form you can add the field to your subscription form to collect your subscribers country.