There isn't currently an automatic process for doing that. You might contrive a way to accomplish what you want using tags and the Zotero search. But you would need to do a great deal of manual editing of your records.

Consider that many articles may be clearly about what occurs in a country but without mentioning the name of the country. The literature contains umpteen articles about things affecting citizens of Beijing, Mumbai, New York, etc. without mentioning China, India, or the USA. This will be possible when/if Zotero implements some sort of thesaurus hierarchy as a search query tool. Even then, context and 'training' would be involved before such a system would be useful to _you_ as opposed to someone else. There is a body of journal articles that refer to 'Ontario' without further specification. In my example these are about Ontario, California (a small city with a major airport) and not the larger body of literature concerning the Canadian province. There will be a need for a system of disambiguation of terms (USE/OR in thesaurus construction parlance).

edit: The Ontario articles were authored by someone from a nearby university and this ambiguity wasn't recognized by journal reviewers or the editor. The articles concerned brain concussions from youth "football". Knowing that the articles concerned schools in California this meant American tackle football was the topic. However, if a reader didn't see the author's affiliation it could be thought that the articles were about Canadian football (a game with quite different rules and risks) or even association football (soccer). This double-confusion of place and topic couldn't be handled automatically.

In CSV file it shows the country do we have place to enter the country manually