Step 1: Comparative reframing:
Compare failed single-criterion definitions: if 'nation' meant 'one language,' India (many languages) would not qualify; if it meant 'one religion,' most modern nations would not qualify either, showing no single test works.
Final Answer:
Since no single objective criterion consistently identifies a nation, and national identity is a matter of shared political feeling rather than a fixed trait, a precise, universal definition is inherently difficult.