"Europe is not a country."
Translation:Europa nie jest krajem.
"Something is not a..." - instrumental
"There is no..." - genitive
"Somebody didn't do..." - genitive
"I can't take/see something" - genitive
With the verb "być" (to be), the object takes the Instrumental case whether it’s negated or not. Most other verbs (but not all) take the object in the Accusative case when not negated and in the Genitive case when negated.