In 1940, the major comic producers of the time: Fawcett, DC, MLJ and Marvel all decided to produce assortment comics containing their superheroes. The comics titles were, in order: 'America's Greatest', 'All Star', 'Jackpot' and 'All Winners'. A sound idea that I personally wish they had maintained.
DC's 'All Star' was the first to hit the streets, though they all appeared inside a two month gap.
In our case it was the third issue of 'All Star' that is of interest, as it included the first meeting of the 'Justice Society of America'. This featured two characters from each of four anthology comics — The Flash and Hawkman from Flash Comics, Green Lantern and The Atom from All American Comics, Dr. Fate and The Spectre from More Fun Comics, and Hourman and The Sandman from Adventure Comics. Johnny Thunder (from Flash) and The Red Tornado (from All American) were uninvited guests. (Johnny became an actual member in All Star #6.)
Both Superman and Batman being given 'honorary membership', paying periodic membership, whilst Wonder Woman was actually allowed to join a few months later.
Other occaisional and not so occaisional members included Wildcat (sort of Batman rip off), Starman (Superman rip?), Dr Mid-Nite, Mr Terrific, Black Canary. (Fury and Miss America, featured in the 1985 retro comic were not members in the original!)
The JSA out lived most of its members individual series, lumbering on until 1951, when the comic became 'All Star Western', featuring cowboy heroes, The Trigger Twins, Strong Bow and a new Johnny Thunder. All deeming the end of the JSA, for a while at least.
Or until 1956, when All Star returned with superheroes, Flash and Green Lantern and finally with a mottley selection of others to produce the Justice League.
Of course comparison between the JLA and the JSA was inevitable. With the result that the JSA are regularly brought from retirement to aide their younger counterparts.
Other spin offs come in the form of 'Infinity Inc' a second-generation JSA featuring the offspring of the JSA members and 'All-Star Squadron' a complete retro-series based in the 1940's, featuring not only the JSA but every other hero and anti-hero in the DC stable of the time (lots).
Check out http://www.execpc.com/~icicle/JSAHOME.html
http://www.toonopedia.com/jsa.htm