If you would like to only offer free shipping to some of your customers(country-specific), you can use the Rebuy Smart Carts free shipping bar to do so! Login to the Rebuy Admin then navigate to the Smart Cart tab! Enable Free Shipping, then check "Only available for certain countries". Once you check this, you can add country-specific codes and it will only show for people in that geo location!
If you haven't setup the smart cart yet, checkout this awesome help doc to get started Rebuy Smart Cart!