Write SQL query to solve given problem: Calculate the percentage of countries that belong to the American region.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(IIF(T1.r_name = 'America', 1, 0)) AS REAL) * 100 / COUNT(T2.n_name) FROM region AS T1 INNER JOIN nation AS T2 ON T1.r_regionkey = T2.n_regionkey