What single word (≤7 letters) completes all blanks in this countries chart?

TheChart of Most and Least Countries
TheChart of Most and Least Countries

I'm back from my month-long European vacation...

With an interesting question.

The attached chart shows a list of the MOST and LEAST countries in a particular category.

Each of the three white boxes can all filled with the same word to make the chart make sense.

Using the information in the chart, can you add the correct word?

Correct answer will be given in a few days, Wednesday.

Hint: The word is no longer than 7 characters.

Updates
1 mo
The missing word is FREE.

Congratulations to those who got it.
What single word (≤7 letters) completes all blanks in this countries chart?
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