This is the 66th most frequent Russian word.
стран
Genitive plural form of "страна," meaning "countries" or "of countries."
In this sentence, 'стран' ('countries') is used in the genitive plural form to indicate possession or relation.
Многие стран мира объединяются для сохранения мира.
Many countries of the world unite for maintaining peace.
Here, 'стран' serves as a genitive plural complement to denote origin or affiliation.
В музеях стран можно увидеть уникальные экспонаты.
In the museums of the countries, one can see unique exhibits.
In this example, 'стран' in the genitive plural form represents a relationship, describing that the resources belong to the countries.