The origin of the JLA was revealed in Justice League of America Vol 1 #9 when seven heroes first came together to repel the Appelliax alien invasion. When the world's greatest heroes were unable to defeat this alien threat individually, the Martian Manhunter, the Flash (Barry Allen), Green Lantern (Hal Jordan), Wonder Woman, Aquaman, Superman and the Batman cooperated together as a team to defeat the Appelliax invaders. These heroes continued to work together as the Justice League of America, after realizing they worked well together and getting backing and support from the American government. Later on after Crisis on Infinite Earths, Black Canary was reconnected as a founding member in Wonder Woman's place. The new 52 version of the team has a new canonical origin, which is virtually the same except that it was Darkseid that was invading the Earth and that Cyborg has replaced the Martian Manhunter as a founding member.
Creation
After the successful revival of superheroes in the Silver Age, DC Comics tasked Gardner Fox and Mike Sekowsky with the job of reviving the Golden Age's Justice Society of America. Fox was inspired by the word League in various sports franchises at the time and decided to create a new name as well as a new team by replacing Society for League. Fox and Sekowsky created the Justice League of America in 1960 and crafted the story and pencils for the team's first appearance in the Brave and the Bold #28. Murphy Anderson was also the inker for this issue.
Although Superman and Batman made appearances as members of the JLA in this debut, they were not involved in the main story line or battle with Starro the Conqueror. The other five members of the League battled Starro seeking to free the citizens of Happy Harbor, Rhode Island from his mental influence. Lucas "Snapper" Carr who was immune to Starro's powers became an honorary member of the JLA.
Fox, Sekowsky and Anderson created two more stories starring the JLA in the Brave and the Bold #29 and #30 and then became the creative team for the early years of the JLA's on-going title.
Team Evolution
Silver Age (1960s) & Bronze Age (1970s-1980s)
During the last decade of the Silver Age, DC Comics established that the JLA came from Earth-1. The JLA maintained their first headquarters in a cave called the Secret Sanctuary in Happy Harbor, Rhode Island. The JLA had an annual tradition of team-ups with their Golden Age counterparts, the Justice Society of America from Earth-2, that started in Justice League of America Vol 1 #21. During one of these team-ups, the JLA and the JSA encountered a villainous version of themselves called the Crime Syndicate of America from Earth-3. The JLA added other members to the original line-up to include Green Arrow, the Atom (Ray Palmer), Hawkman and Black Canary.
The membership of the JLA remained consistent from the Silver Age to the Bronze Age. The sole exception to this was with Wonder Woman, who left the League during her depowered phase in the late 1960s. She would rejoin a short time later however after regaining her powers. The JLA moved their headquarters to the Justice League Satellite when Snapper Carr unknowingly compromised the location of the Secret Sanctuary. The JLA Satellite had a geosynchronous orbit 22,300 miles above the Earth. The regular team-ups between the JLA and the JSA featured the return of other Golden Age heroes such as the 7 Soldiers of Victory and the Freedom Fighters. The JLA and the JSA had a time-travelling adventure with the Legion of Super-Heroes caused by Mordru.
During the 1970s, Elongated Man, Red Tornado, Hawkgirl and Zatanna officially joined the JLA. The Phantom Stranger officially joined the JLA during this time as well though his active status was hardly noticeable as the Stranger mostly appeared at events of a cosmic nature. In 1980, Firestorm was the final recruit to join this roster of the JLA. In 1983, the Batman resigned from the JLA due to the team's refusal to embark on a rescue mission into Markovia. The Batman then formed his own team called the Outsiders.
The roster of the JLA maintained this membership through the early 80s until the events of a Martian invasion in Justice League of America Vol 1 #228-230. In the aftermath of repelling the invasion, the JLA Satellite became severely crippled and current members demoralized and despondent about the team's future status. Aquaman decided to take a stand that the JLA needed full-time members who did not leave to fulfill obligations in their civilian identities. The result was the departure of several members and the end of this roster.