This is the 1673rd most frequent Russian word.
сирии
"Сирии" is the genitive or dative case form of "Сирия," meaning "Syria" in English.
In this sentence, "Сирии" is the genitive case of the noun, indicating possession or relation ('of Syria').
Я изучаю историю Сирии.
I am studying the history of Syria.
Here, "Сирию" is the accusative case of the noun, used to indicate the destination of the action (travel).
Мы отправимся в Сирию на следующей неделе.
We will travel to Syria next week.
"В Сирии" uses the prepositional case with the preposition 'в', indicating location ('in Syria').