Simplify the following text for a Grade 9 native English-speaking person.
Original: Opera seria was less popular in France , where the national genre of French opera was preferred . Popular composers of opera seria included Alessandro Scarlatti , Johann Adolf Hasse , Leonardo Vinci , Nicola Porpora , George Frideric Handel , and in the second half of the 18th century Tommaso Traetta , Gluck , and Mozart .
Simplified: One of the first composers of opera seria was Alessandro Scarlatti .