If you want a campaign to trigger only to visitor from a specific country or countries, you should use the Countries setting. By default, visitors from all countries will see the campaign. 

You can include the countries you want or exclude the ones you don't want your campaign to run.

After you enter the country you want to target, you have the option to target specific areas or cities within this country. 

Here is an example targeting only the London and Manchester area in the UK.