A more thorough explanation:

A nation-state is a group of people who share a common history, language, and traditions and are organized under an independent government. When a nation and a state are the same, it is called a nation-state.

For example, Japan is a nation-state because the Japanese people share a common language, culture, and history, and they are organized under the government of Japan. On the other hand, the United States is not a nation-state because it is made up of many different ethnic and cultural groups, and it is organized under a federal government.

The concept of a nation-state is important because it helps to define the boundaries of a country and the identity of its people. It also helps to create a sense of unity and belonging among the citizens of a country.