Northwest Airlines Corp. (NWA) was a major American airline founded in 1926 and absorbed into Delta Air Lines, Inc. by a merger. The merger, approved on October 29, 2008, made Delta the largest airline in the world until the American Airlines-US Airways merger on December 9, 2013. Northwest continued to operate under its own name and brand until the integration of the carriers was completed on January 31, 2010.Northwest was headquartered in Eagan, Minnesota near Minneapolis-St. Paul International Airport. After World War II it became dominant in the trans-Pacific market with a hub in Tokyo, Japan (initially Haneda Airport, later Narita International Airport). In response to United Airlines's 1985 acquisition of Pan Ams' Pacific routes, Northwest paid $884 million to purchase Republic Airlines and then established fortress hubs at Detroit Metropolitan Wayne County Airport and Memphis International Airport. With this merger, NWA established the domestic network necessary to feed its well established Pacific routes. Lacking a significant presence in Europe, in 1993 it began a strategic alliance with KLM and a jointly coordinated European hub at Amsterdam Airport Schiphol.

Prior to its merger with Delta, Northwest was the world's sixth largest airline in terms of domestic and international scheduled passenger miles flown and the US's sixth largest airline in terms of domestic passenger miles flown. In addition to operating one of the largest domestic route networks in the U.S., Northwest carried more passengers across the Pacific Ocean (5.1 million in 2004) than any other U.S. carrier, and carried more domestic air cargo than any other American passenger airline.Regional and commuter airline flights for Northwest were operated under the name Northwest Airlink by Big Sky Airlines, Eugene Aviation Services, Express Airlines I/II, Fischer Brothers Aviation, Mesaba Airlines, Northeast Express Regional Airlines, Pacific Island Aviation, Pinnacle Airlines, Precision Airlines, Simmons Airlines and Compass Airlines via respective code sharing agreements. Northwest Airlines was also a minority owner of Midwest Airlines, holding a 40% stake in the company.Northwest Airlines' tagline was "Now you're flying smart." Its frequent-flyer program was called WorldPerks.

Delta Air Lines, Inc., typically referred to as Delta, is one of the major airlines of the United States and a legacy carrier. One of the world's oldest airlines in operation, Delta is headquartered in Atlanta, Georgia. The airline, along with its subsidiaries and regional affiliates, including Delta Connection, operates over 5,400 flights daily and serves 325 destinations in 52 countries on six continents. Delta is a founding member of the SkyTeam airline alliance.Delta has nine hubs, with Atlanta being its largest in terms of total passengers and number of departures. It is ranked second among the world's largest airlines by number of scheduled passengers carried, revenue passenger-kilometers flown, and fleet size. It is ranked 69th on the Fortune 500. The company slogan is "Keep Climbing."