Simplify the following text for a Grade 7 native English-speaking person.
Original: The Goryeo Dynasty or KoryÅ ( 918-1392 ) was a Korean sovereign state established in 918 by Emperor Taejo .
Simplified: The Goryeo Dynasty also called the `` Kingdom of Goryeo '' , is one of the Korean dynasties which existed from 918 to 1392 . It began in 918 with Emperor Taejo .