In Discount Ninja free shipping promotions you can set up a Shipping zone.
This ensures that the free shipping is only applied if the customer ends up shipping to countries that are in the selected Shipping zones. This is enforced by Shopify at checkout when customers enter the shipping address. If they choose to ship outside of the shipping zone associated with the promotion, your standard shipping rules will apply.
To set this up, create a promotion of the following type:
Then, scroll down in the Offer tab and set a Shipping zone:
Restrict access to a promotion based on IP address
You can, optionally, also restrict a promotion based on IP address geolocation: this is set up in the Trigger section, under the Targeting tab. Set "Country" to ON and select the countries that should be in/excluded:
This ensures that a customer is not offered a specific promotion when they are (not) connecting from a specific country. This can be useful to avoid offering promotions to customers that are likely not eligible.