This is the 12151st most frequent Russian word.
иммиграцией
Immigration.
The word "иммиграцией" here is used as the instrumental case of the noun "иммиграция" (immigration), indicating the means or subject of interest.
Он интересуется иммиграцией в Канаду.
He is interested in immigration to Canada.
In this context, "иммиграцией" is used to denote the subject being discussed, emphasizing its role in the discussion.
Проблемы, связанные с иммиграцией, обсуждают на международной конференции.
Issues related to immigration are discussed at the international conference.
Here, "иммиграцией" functions as the object of the verb "занималась" (was dealing with), presented in the instrumental case indicating the matter of her focus.