The phrase "cluster of countries" is correct and usable in written English.
You can use it to refer to a group of countries that are geographically close together and/or share certain political and social characteristics. For example, "The European Union is a cluster of countries that have agreed to cooperate economically and politically."
There is also a cluster of countries in eastern and northern Africa.
The chart shows a cluster of countries at the bottom where the food supply barely changed in 50 years.
Related Internet content-control mechanisms are also in place in Canada, the United States and a cluster of countries in Europe.
A single governor would represent a cluster of countries: the Estonian governor, say, would vote for the Baltic States, and so on.
A terrific map called "New York Global Island" (unfortunately printed on too small a scale to be readable) recreates Manhattan as a cluster of countries in mostly accurate positions, China in Chinatown being one.
A terrific map called "New York — Global Island" (unfortunately printed on too small a scale to be readable) recreates Manhattan as a cluster of countries in mostly accurate positions, China in Chinatown being one.
The evaluability assessment concluded further, that there is significant variation even within each cluster of country programmes.
From the structural topologies of these trees, we identify different clusters of countries according to their geographical location and economic ties.
The second part of the analyses indicates the basic and post school entrepreneurial education and training clusters of countries.
The maps indicate that there has been an increasing concentration of African migrant populations in particular countries or clusters of countries.
Even though non-traffic-related NO x can make up half of the aggregate NO x emissions in most countries, a prominent clustering of countries with both highest NO x threshold value exceedances and highest share of diesel cars in their fleets is observed (Figure 3).
