It’s a little unlikely that you’ll have only one country for worldbuilding. Although your story or even your game campaign may only take place in one particular country, as a general rule humans don’t do great in massive cohesive groups. Add in a couple of different races and you’re almost certain to have at least a couple of different countries in your world.
Where you have multiple countries, you also have multiple chances for conflict. Politics is often the basis of how a group of people govern themselves. When you have different groups, you often have different ideas of how they should be governed. In itself that can be the basis for conflict between countries. Resources are yet another place where varied opinions might clash—that includes not only food or minerals, but also land.
A good way to manage multiple countries might be to figure out where their conflicts potentially lie. Start with cultural differences. Do they have differing religions? What about language? Are there certain actions which might be considered respectful in one culture, but odd or even insulting in another?
Now consider the resources your countries have. Animals, plants and building materials are major resources for civilization at any stage. Following that, decorative items such jewels or dyes are often traded back and forth.
With your resources and cultures figured out, look at how well they can be meshed together. If one country is drowning in a particular resource the other one considers holy, it’s possible trade agreements will be reached. This is where imports and exports come in. Countries doing a lot of trade are likelier to set aside their differences and may form alliances in times of war. Keep in mind this isn’t always the case—owing another country a lot of money doesn’t breed much goodwill on either side.
A final thing to consider is how easily people can immigrate from one country to another. How easy is it for citizens of one nationality to becomes citizens of another? What steps do they have to take, and how does this changed based on which country they’re coming from and going to?