Northwest Airlines Corp. (often abbreviated as NWA) was a major United States airline founded in 1926 and absorbed into Delta Air Lines, Inc. by a merger. Approved on October 29, 2008, the merger 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). After acquiring Republic Airlines in 1986, Northwest also established major hubs at Detroit Metropolitan Wayne County Airport and Memphis International Airport. In 1993 it began a strategic alliance with KLM and a jointly-coordinated European hub at Amsterdam Airport Schiphol. The Detroit and Minneapolis operations were retained as Delta hubs. However, the Memphis operation peaked at more than 300 flights per day prior to the merger with Delta.

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.

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