A nation is a large group of people who share a common identity, often including things like language, culture, history, or traditions. The people of Japan form a nation because they share Japanese language and culture. The Jewish people are considered a nation because they share thousands of years of history, religion, and traditions, even though they've lived in many different places around the world.

Nations are not the same as countries, though we often use the words interchangeably. A country (or state) is a political entity with defined borders and a government, while a nation is about shared identity and belonging. Sometimes a nation and a country match up perfectly: Japan is both a nation and a country. But sometimes they don't: the Kurdish people form a nation spread across several countries in the Middle East, and the United Kingdom is one country containing multiple nations (English, Scottish, Welsh, and Northern Irish).

When we talk about a nation-state, we mean a country where most people belong to the same nation. The United States is unusual because it's not based on a single ethnic or cultural nation but on shared ideals and values, making it a civic nation where people can become American by embracing those principles.