Simplify the following text for a Grade 9 native English-speaking person.
Original: Northwest Airlines , Inc. ( often abbreviated NWA ) , was a major United States airline headquartered in Eagan , Minnesota , near Minneapolis-St .
Simplified: Northwest Airlines , Inc. ( often abbreviated NWA ) is a subsidiary of Delta Air Lines , Inc. , and is a major United States airline headquartered in Eagan , Minnesota , near Minneapolis-St .