Which region has the lowest number of countries?
region refers to has r_name; the lowest number of countries refers to min(count(n_name))
SELECT T.r_name FROM ( SELECT T1.r_name, COUNT(T2.n_name) AS num FROM region AS T1 INNER JOIN nation AS T2 ON T1.r_regionkey = T2.n_regionkey GROUP BY T1.r_name ) AS T ORDER BY T.num LIMIT 1