With the Justice League of America, Julius Schwartz and Gardner Fox had something of a problem. During the JSA's run in All-Star during the Golden Age, comics were larger and thus could accommodate what were essentially separate adventures for the various heroes with a plotline that somewhat loosely tied them together. With the smaller comics of the Silver Age (essentially 25-page stories) and five heroes and the need for intros and outros, it didn't make much sense to have individual storylines. As a result the general setup was for 1-2 heroes in separate chapters. However, this created another problem; given that no DC villains had ever defeated even one hero in a story, how could Schwartz and Fox create drama with a villain facing two heroes?
In Brave & Bold #28 (the first JLA story), the answer was to have an alien villain, Starro the Conqueror. Starro looked like a giant starfish, and so he deputized three Earth starfish. They battled Green Lantern, the Martian Manhunter and Wonder Woman, and the Flash, respectively. In the finale, all the members ganged up to defeat Starro.
In B&B #29, the JLA faced the Weapons Master, a villain from the future who was trying to figure out which of four amazing weapons he had would defeat the police of his era. So he came back in time and battled the JLA. First he took on the Flash, then Martian Manhunter and Aquaman, then Wonder Woman and Green Lantern. In the final chapter, all the JLA members (including Batman and Superman) defeated the Weapons Master.
In the final tryout in B&B #30, the villain was Amazo, the android who could absorb the powers of the JLA. In the first segment, he defeated Wonder Woman. The second chapter had him beating Green Lantern and Aquaman, while in part three he managed to top Flash and the Martian Manhunter. In the finale, Green Lantern manages to defeat him.
Rather than continue on discussing the individual segments, I'll just talk about the villains and why they were able to handle the JLA:
In JLA #1, Despero (an alien) puts all the JLA members except the Flash into a trance. Then he plays a bizarre game of chess, which results in each of the members being transported to face a menace on an alien world. Thus he really doesn't have to battle the JLA as a team or even individually.
In JLA #2, there are three villains, all of whom use magic to battle the superheroes.
JLA #3 features the first appearance of Kanjar Ro (an alien), who immobilizes everybody on Earth and blackmails the JLA into helping him in his battles with the rulers of three other planets.
In JLA #4, the team faces an alien with amazing weapons.
Doctor Destiny uses robots that are constructed to look like foes of the JLA members and stays in the background until he can use a will-deadening ray on them in JLA #5.
In JLA #6, Professor Amos Fortune invents the Stimoluck, a machine that can cause people to have a run of bad luck.
In JLA #7, aliens use an energy-sapping device.
A small-time crook discovers a flashlight which can force others to obey his commands in JLA #8.
In JLA #9 aliens with weird powers battle the Justice League.
Felix Faust uses magic against the JLA in #10.
Overall, in the thirteen issues, there are six battles against aliens. But even more common than the aliens are the bizarre weapons, which appear in almost every issue when you think about it. B&B #29 and #30 (Amazo the android is a weapon), JLA #4, 5, 6, 7. You can talk about the aliens, but they are mainly there because they bring credibility to the oddball weapons.
This post was suggested in an email by longtime commenter Warren.