Questions & Answers about Магия исчезла.
магия is the subject: magic.
исчезла is the verb: disappeared / vanished.
So the structure is simply:
subject + verb
Магия исчезла. = Magic disappeared.
It is in the nominative case because it is the subject of the sentence — the thing that disappeared.
Dictionary form: магия
Nominative singular: магия
If it were a direct object, it would usually be in another case, but here it is the one performing the action of disappearing, so nominative is used.
In Russian, магия is a feminine noun. One clue is its ending: nouns ending in -а or -я are very often feminine.
So:
- магия = feminine singular noun
That matters because in the past tense, Russian verbs agree with singular subjects in gender.