Answer:
A nation-state.
Step-by-step explanation:
A nation-state is a sovereign polity or state that has a specific territory with clearly defined borders. It also has citizens, laws, and government that presides within that premise. In other words, a nation-state is when a whole nation has a state of its own, predominantly occupied by a single cultural section of people.
An example of a nation-state is Japan, China, North and South Korea, Portugal, etc.