This is the 10882nd most frequent Turkish word.
devletlerin
"Of the states" (possessive form).
The word 'devletlerin' is used in its possessive plural form to indicate that the relations belong to multiple states.
Tarih boyunca devletlerin ilişkileri ekonomiyi etkilemiştir.
Throughout history, the relations between states have affected the economy.
Here, 'devletlerin' indicates the ownership of cooperation that belongs to the states involved in such agreements.
Ülkeler arası anlaşmalar, devletlerin işbirliğini artırabilir.
Agreements between countries can enhance cooperation between states.
In this sentence, 'devletlerin' is used to specify the states whose policies are being referred to, in a possessive plural form.