Sentence:  When we look at countries like Iran , Iraq , Pakistan , and Burma , where substantial progress has been made in creating a minimum supply of modern men and of social overhead capital , and where institutions of centralized government exist , we find a second <WSD>category</WSD> of countries with a different set of problems and hence different priorities for policy . 
Meaning of the word marked with <WSD> tags:  a collection of things sharing a common attribute