This is the 646th most frequent Turkish word.
ülkeyi
"Ülkeyi" means "the country" (in the accusative case) in English.
In this sentence, 'ülkeyi' is in the accusative case, acting as the direct object of the verb 'etkileyebilir' (might affect).
Deniz seviyesinin yükselmesi ülkeyi etkileyebilir.
The rise in sea level might affect the country.
Here, 'ülkeyi' is again in the accusative case, denoting the direct object receiving the action of being introduced in the context of the verb.
Öğretmen, öğrencilere ülkeyi tanıtan bir film gösterdi.
The teacher showed the students a film introducing the country.
The word 'ülkeyi' is used here as the accusative form of the noun 'ülke' (country), indicating that it is the direct object of the verb 'gezen' (visiting).