Write SQL query to solve given problem: What percentage of films are made in the US?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(COUNT(CASE WHEN T3.COUNTry_iso_code = 'US' THEN T1.movie_id ELSE NULL END) AS REAL) * 100 / COUNT(T1.movie_id) FROM movie AS T1 INNER JOIN production_COUNTry AS T2 ON T1.movie_id = T2.movie_id INNER JOIN COUNTry AS T3 ON T2.COUNTry_id = T3.COUNTry_id