What were the little events and plots on which The Marvel Universe was built?

[DrNewGod]

One of the things I loved about Marvel was always the coherency of its shared setting. Sure there were gaffs here and there, and some characters seemed to dwell in an MU that was more congruent with, than part of the rest (i.e. Dr. Strange), but it was this big, vast interconnected world with a common history that mattered. Most fun of all, most of that stuff congealed over time as writers filled in holes or made use of one another's creations.

I'm not talking about the huge ones, like "The Kree-Skrull War," where Thomas was deliberately stitching previously disparate pieces of the environment together. I'm talking about the seasonings, rather than the entrees. What were the small things that helped pull the MU together and make it whole.

One of my early favorites was The Amazing Spider-Man 16, where the title character, and a new-comer/guest-star (Daredevil) windup tangling with a Hulk villain (Ringmaster and his Circus of Crime).

Another was Peter Henry Gyrich. He went from being a plot point about how governments might react to an organization like the Avengers, to a point-man on the mutant witch hunts, to an all-purpose government fixer-type that might appear anywhere.

[Electricmastro]

1963 saw the first Marvel Silver Age crossover with the Hulk appearing in Fantastic Four #12. This is followed with the FF's appearance in Amazing Spider-Man #1, and then an Ant-Man appearance in Fantastic Four #16. We also start to see villains moving between books, as Dr. Doom shows up in Amazing Spider-Man #5, and the Human Torch fights the Sandman in Strange Tales #115.

[DrNewGod]

D.A. Tower was a handy binding element.

[Revolutionary_Jack]

The most emblematic of these small moments you talk about is FF#4.

Kirby Namor.jpg

This moment has Johnny Storm run into a random hobo in the Bowery and then give him a shave and we find out that it's Namor the Submariner.

This panel is important for several reasons:
-- It established that Fantastic Four was in direct continuity to the Golden Age Timely Era comics.
-- It established an entire backstory and pool of heroes and characters for writers/artists to refer to.
-- It set the stage for Captain America's revival since the Captain America comics were now in continuity since Cap did cross over with Namor in the Timely Era.
-- It established that World War II and real-history was the backstory of the present-day Marvel Age, so that set the stage for say Wolverine crossing over with Cap, Magneto being a Holocaust survivor and so on.

All of that comes from this page. Alan Moore once said that this was one of his all-time favorite moments in comics. Because it established that the great Namor was now an unrecognizable hobo, that time had passed and that he had been forgotten somewhat, and that inspired his own Deconstructive stories and informed his ideas about what happens if superheroes age and grow old.

Other examples is as mentioned by Electricmaestro, ASM#5, this was Doctor Doom's first appearance outside Fantastic Four, and it established him and canonized him as Marvel's great overarching villain.

GIANT SIZE X-MEN #1 is another seminal issue of immense importance. It's essentially the new beginning of X-Men.