I am rereading the entire original Avengers run. Noticed something I missed in childhood:
In the first several issues, the Avengers mostly fight themselves. For the record, the founding Avengers are Thor, Iron Man, Hulk, Ant-Man, and the Wasp, though she does not get cover billing. She is, however, the one who technically names the team. (I am still irked that the Avengers movie not only follows the Ultimates version, but also ignores both it’s own and the original founding members.)
In the initial books, the Avengers are mainly fighting the Hulk. This goes on for a while, never his fault. No wonder he is angry.
In the first issue, this Hulking misunderstanding is caused by Loki, hence the classic cover (and revised origin for the movie version).
An aside: the first issue has the Hulk incognito as a circus clown, something I hope to never see again.
In the second issue, the interdimensional Space Phantom supplants the Avengers one-by-one and causes them to fight amongst themselves, but, again, mainly against the Hulk. This so angers Hulk that he quits the team.
In the third issue, the Hulk teams with the Sub-mariner in mutual hatred of the Avengers. They attack and almost succeed in destroying the Avengers.
Sub-Mariner is barely driven off (he is extremely powerful), and in anger at his defeat he goes on a polar rampage. This leads to the perhaps most momentous issue of all Avengerdom, number 4. Sub-Mariner has unwittingly broken up a glacier which hid the frozen body of Captain America, who then thaws and returns to join the team.
In all the early books, there is only one actual major Earthly supervillain: Baron Zemo. Baron Zemo is a relic from Cap’s WWII years and has apparently been hiding in the Amazon ever since the Nazi’s defeat. Zemo returns to global villainy because of the return of Captain America.
I refuse to label evil the angry, antihero associates, the Hulk and Sub-Mariner, or the misunderstood Lava Men of issue 5. The other villains of the books are meddling gods, aliens, or time travelers.
So, Baron Zemo returns in issue 6. He creates an enduring supercriminal team to fight the Avengers, the Masters of Evil. This makes Baron Zemo the preeminent supervillain of the Avengers, which is odd because except for being a glue-headed ex-scientist criminal mastermind, he is perhaps the weakest villain. His threat continues in issue 7, though, due to the aid of the Enchantress and Executioner of Asgard.
Issue 7 also begins with another powerful moment which shows the problematic nature of the team. Iron Man is suspended for refusing to answer the Avengers alarm is suspended from the team. These types of member dramas (echoing the Hulk’s tumultuous, short-lived, founding run) will recur throughout the entire series. Again, these have nothing usually to do with supervillains, just personal issues or in-fighting in some cases.
Not until issue 8 do we have an exceptionally powerful threat from Kang the Conqueror. He is so powerful he quickly brings the world to its knees, including the Avengers, and is not so much defeated as tricked. His threat is shunted, as it were, into the future.
In 9, Baron Zemo returns with Wonder Man, then follows with a pact with Immortus in issue 10.
So in the first ten, four of the books are Baron Zemo’s, one Kang, one the Lava Men, and the rest are in-fighting, albeit often caused by outside sources. On top of this, by issue 16 the founders all take a leave of absence because, as Wasp says, they, “…are tired of all this fighting….” This leaves Captain America alone and responsible for forming an entire new lineup.
The team history truly sets the stage for the later Civil War.