Minnesota, Wisconsin, Illinois, Indiana, Ohio, and Michigan was originally called the "Northwest Territory" before being slowly divided up into states. It was the original northwestern area of the young United States.

There is also Northwestern University in Chicago.

NWA's original flights were mostly NYC, DTW, CHI, MKE, MSP, etc. towards the "newer" northwest region of the Dakotas, MT, ID, WA, OR, AK, etc.

Flights were awarded to airlines in the US based alot on regionalism, hence: Northwest, Southwest, Western, Eastern, Northeast, Southern and North Central Airlines. Sort of like how it's in China today. They're just names of where their preponderance of flights were. Most are gone now, just SWA and NWA remain.

NWA has a Memphis hub from its merger with Republic Airlines.

In case you didn't know, NWA started in 1926, later using the name "Northwest Orient Airlines."

Bonanza, West Coast, and Pacific Airlines became AirWest then Hughes AirWest.

Southern and North Central Airlines became Republic Airlines.

AirWest and Republic merged to form a larger Republic Airlines.

Republic and Northwest Orient merged to become NWA.

If a US airline didn't have a "regional" name, they then usually had something patriotic, democratic, or American-sounding, hence: Republic, United, American, Liberty, etc.