This is the 1679th most frequent Turkish word.
ülkelerin
"Of the countries" or "countries'".
Here, 'ülkelerin' is used in possessive-genitive form to indicate possession (the development of countries).
Ülkelerin gelişmesi eğitime yapılan yatırımlara bağlıdır.
The development of countries depends on investments in education.
In this sentence, 'ülkelerin' is used in possessive-genitive form to connect 'economies' with 'countries' (the economies of countries).
Ülkelerin ekonomileri küresel pazarlardan etkilenir.
The economies of countries are affected by global markets.
Here, 'ülkelerin' is used to define the entities involved in cooperation (countries collaborating).