Explanation:

Let's break it down:

- Territory: This is the physical land within defined borders that a nation-state occupies. It's where the government exercises its authority.

- Sovereignty: This is the full right and power of a nation-state to govern itself without any interference from outside sources or bodies.

- Government: This refers to the political and administrative organization that runs the state's affairs, making and enforcing laws.

- Ethnicity: Here's the thing: Ethnicity isn't a necessary element of a nation-state. Nation-states often have multiple ethnic groups within them.

So, to answer: Ethnicity is not a necessary element of a nation-state.

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