If you want to target specific countries for your campaign and exclude all others, you can use the geotargeting feature.

Go to advanced settings > geo-target.

By default, all campaigns are set to be active in all countries.

If you want to target a region or specific country, select either Target a region or the country you want to target and click the Add Selected button. 

Users will be able to see the page, however, if they try to enter from a country that isn't on your allowed list, then they will see an error message. 

When you add a country to your list, all others will become inactive.