This is the 919th most frequent Russian word.
наступления
"Наступления" means "offensives" or "advances" in English.
Here, 'наступления' translates to 'onset' or 'beginning', signifying the commencement of an event (spring).
Зима ожидается перед началом наступления весны.
Winter is expected before the onset of spring.
In this sentence, 'наступления' is used as 'offensive', referring to a military advance or attack.
Во время наступления армии постепенно окружали город.
During the offensive, the armies gradually surrounded the city.
Here, 'наступлении' ('наступления' in another case) refers to the arrival or occurrence of a condition (darkness).