Simplify the following text for a Grade 10 native English-speaking person.
Original: In classical antiquity , Illyria ( Ancient Greek : or ; ; see also Illyricum ) was a region in the western part of the Balkan Peninsula inhabited by the Illyrians , a heterogeneous coalition of tribes .
Simplified: Illyria was a ancient region in the western part of today 's Balkan Peninsula , by tribes of Illyrians an old people who spoke the Illyrian languages .