This is the 1048th most frequent Turkish word.
ülkeleri
"Ülkeleri" means "their countries" in English.
The word 'ülkeleri' is used as a direct object here, indicating the countries being visited.
Farklı ülkeleri ziyaret etmeyi seviyorum.
I love visiting different countries.
The word 'ülkeleri' emphasizes the specific countries being learned about or studied, serving as a direct object.
Bazı ülkeleri öğrenmeye çalışıyorum çünkü onların tarihini ilginç buluyorum.
I am trying to learn about some countries because I find their history interesting.
In this case, 'ülkeleri' is in the accusative form, specifying the countries being compared by the book.