The cover of Avengers Annual #11 asked a good question: Why do the Avengers battle the Defenders?
In this case, the heart of the conflict was a lovers' quarrel between Nebulon and wife Supernalia, who tired of Nebulon's ongoing attempts to take over the Earth (since his debut in Defenders #13-14).
While Nebulon psionically influenced four Avengers to come to his aid, Supernalia persuaded four Defenders to prevent Nebulon's latest scheme.
When the super teams faced each other in battle, they seemed destined for a stalemate, with each pair of combatants about evenly matched.
- Valkyrie vs. Thor
- Silver Surfer vs. Iron Man
- Beast vs. Captain America
- Gargoyle vs. Wasp
The couple's last words revealed that Nebulon finally saw the error of his ways, and Supernalia believed that by sparing the Earth they were dying for a higher purpose.
As a back-up feature, this annual printed the never-before-seen charter of the Avengers, signed by the founding members, with two pages of accompanying by-laws. The informal Defenders, of course, never drafted such a document.
Avengers Annual #11 marked an important turning point for one of the Defenders. Following a trip to Asgard in Defenders #109, Valkyrie returned to Earth near the start of the story in her true Asgardian body (instead of the body of human Barbara Norriss, where her mind had resided since Defenders #4). Now aware of her place as leader of the valkyries, she re-introduced herself as Brunnhilde (her previously-unknown real name). For years the Defenders had treated "Val" as her de facto first name.