Why were there two ongoing D&D magazines, and what distinguished them?

D&D has over its history been accompanied by two core supplemental magazines:

  • Dragon magazine, starting in March 1975.
  • Dungeon magazine, starting in September/October 1986.

Both went on hiatus in December 2013, Dragon pausing at issue 450 and Dungeon at issue 221, enjoying an impressive lifetime of 38 and 27 years respectively. (Dragon was later reincarnated in the form of “Dragon+”.)

Something’s always nagged at me me: why were there two magazines, and what was different about them?

What had them start up Dungeon magazine, and also keep it around for so long? What was different about them such that they didn’t just publish more Dragon issues? Was there some substantial characteristic difference in their content, release schedules, etc? Were there substantial market pressures which had them continue two side-by-side magazines instead of just the one?

Was it just “we’d like to sell more magazines, and our game has a second word in it we can use”, or was there far more to it than that?