In November of 1940, German Chancellor Adolf Hitler acquired a powerful mystic weapon known as the Spear of Destiny. With it, he intended on manipulating its power to dominate all of Europe. A British officer named Smythe learned of Hitler's plans and informed American president, Franklin Delano Roosevelt. Roosevelt, pressured by Congress to maintain an isolationist stance, refused to openly involve the United States in England's war with Germany. Instead, he selected two "Mystery Men" from a top-secret dossier to use as civilian agents against Hitler's forces – the Flash and the Green Lantern.
Summoning both men to a special office in Gotham City, Agent Smythe outlined the nature of their mission and told them to fly to McMurdie Castle in Scotland. McMurdie was the site of a special Nazi operation led by an officer named Major Streicher. Streicher's scientists developed a giant robot, known as the Mordmaschine (the Murder Machine). Arriving at the Nazi keep, the Murder Machine proved more powerful than either of the heroes expected and it quickly incapacitated them. Streicher sent the Flash and Green Lantern's unconscious bodies to Berlin, Germany – a gift for the Führer.
Prostrating before the ranks of the German Army, Hitler proudly displayed the captive heroes before the masses. He then used the Spear of Destiny to conjure an army of Norse Valkyrie. The Valkyries were to act as escorts for a prototype long-range bomber that targeted Washington D.C. Green Lantern and the Flash broke free of their bonds and fought the Valkyries, but were unable to prevent the bomber from taking off.
Meanwhile, the sorcerer known as Doctor Fate discovered that Hitler was in possession of the Spear of Destiny. He knew that such a weapon in the hands of a tyrant could only spell destruction for the entire world. Perceiving an imminent Nazi invasion of England, Doctor Fate enlisted the aid of other so-called Mystery Men including, the Atom, Hawkman, Hourman and the Spectre. Fate's magic teleported the heroes to the White Cliffs of Dover where they assisted the British soldiers in fighting off the Nazi hordes. The Spectre single-handedly demolished a fleet of Nazi warships.
With England's shores temporarily safe from enemy attack, the heroes met up with the Flash and Green Lantern, who in turn warned them of the bomber attack on Washington. They followed the plane back towards the United States, and Green Lantern succeeded in destroying it with his ring before it could deploy its deadly payload. However, one of the Valkyries, a warrior named Gudra, managed to evade capture and snuck into the White House. She burst into the Oval Office with the intent of assassinating President Roosevelt. The Atom leapt to his defense, deflecting Gudra's spear, but his heroism proved futile, as Gudra struck again, plunging her weapon into Roosevelt's chest, killing him. Horrified at witnessing the death of such an important American statesman, the Spectre pleaded with the Voice of God to resurrect him. The Voice agreed, but gave warning that Roosevelt was fated to die once more, on the eve of his nation's victory over the Axis powers.
Roosevelt revived, and neither he nor the other assembled heroes possessed any knowledge of the President's passing brush with death. Recognizing that American involvement in Europe was inevitable, President Roosevelt suggested that the heroes should marshal their forces into a cohesive fighting unit aimed at protecting America's home front. Thus, they became known as the Justice Society of America. 
By early 1941, the Justice Society of America had established themselves at a secret hotel room located in Capitol City. Initially, the team was not directly involved in the war against the Axis threat, but they continued to serve the cause by routing out Nazi agents at home, frequently collaborating with the FBI. In one of their first recorded missions, the JSA confounded the efforts of Fritz Klaver, a Nazi collaborator who had led a 5th column organization known as the Grey Shirts.  They also fought up against various non-powered crime figures such as the racketeer Mister X, and the criminal scientist, Professor Alba.
By mid 1941, the JSA roster already began to change and evolve. The Flash stepped down as team chairman, preferring instead an honorary position with the team.  Johnny Thunder was officially inducted into the ranks, followed shortly by Doctor Mid-Nite and Starman. 
On December 7th, 1941, Imperial Japan launched a massive sneak attack against an American military base in Pearl Harbor, Hawaii. This single incident galvanized America's commitment towards the war. As such, President Roosevelt, re-christened the Justice Society as the Justice Battalion for the duration of the conflict. The team functioned as an extended arm of the All-Star Squadron, a massive assemblage of super-heroes dedicated towards preserving the ideals of democracy.
In 1951, Per Degaton embarked upon a scheme to shatter the Justice Society of America once and for all. Operating from behind the scenes, he manipulated several high-ranking members of the Federal government into believing that the JSA had ties to communism. A special inquest convened and the JSA appeared before the House of Un-American Activities Commission (H.U.A.C.). After a lengthy hearing, the committee members demanded that the JSA members reveal their secret identities to the general public. The Spectre (in a showy display of power) vehemently argued on behalf of his colleagues, citing that without their secret identities, they would become targets for enemy agents across the globe. Unwilling to reveal their true faces, the Justice Society instead elected to disband. The public however, never lost faith in their heroes. 
Several members of the JSA continued to operate within the public sector. Starman shared in several adventures with Black Canary, during which the two carried on a brief affair. Eventually, the death of his wife, Doris Lee, caused a complete mental breakdown, and he was forced to give up the mantle of Starman for good.  Former colleague, Charles McNider, having retired his alter ego of Doctor Mid-Nite, briefly carried on the Starman name for a short period in 1951. Note: the role of Starman was also carried on by Ted's future son, David Knight, who traveled backwards in time from the point of his own death in 1994 to the year 1951.
Green Lantern, committed to staying out of the public spotlight, devoted his time towards his career, eventually becoming the President of the Gotham Broadcasting Company. At one point, he became involved with a woman named Alyx Florin, whom he eventually married. Only later did he discover that Alyx was secretly the villainess known as Thorn. Through her, Alan sired two children, the future Infinity, Inc. members, Jade and Obsidian.
Hawkman and Hawkgirl eventually wed, and furthered their archaeological careers. During one of their adventures, they traveled to the mystical kingdom of Feithera where they eventually became the guardians of a young Avian named Norda. They also had their own child, Hector, who, like Norda, would one day join the ranks of Infinity, Inc.
Some time after the formation of the Justice League, the Justice Society also came out of retirement and teamed up time and again with the Justice League on certain missions. It is believed to have started when Barry Allen, who was the Justice League's Flash, first met his Justice Society counterpart Jay Garrick, though the exact circumstances of this encounter are unknown. NOTE: in pre-Crisis history, Barry Allen who was of Earth-1 encountered Jay Garrick of Earth-2 through accidental inter-dimensional travel.
Shortly after returning to active service, the JSA discovered that several more of their old adversaries had come out of retirement as well, notably Brain Wave and Per Degaton. Brain Wave, harboring a new body, was the architect of a series of geological disasters that threatened to destroy the entire world. The JSA responded to the crisis, but found assistance in the form of three younger heroes: Robin, the Star-Spangled Kid, and a new hero named Power Girl. At Power Girl's suggestion, these heroes became an auxiliary detachment of the JSA called the Super Squad. 
Though the Justice Society participated in the event known as the Crisis On Infinite Earths, they began to feel after its conclusion that they were becoming redundant and past their time and so Hawkman called the group together for a unanimous decision to disband. However, just as they were about to finalize the decision, the Spectre appeared unto them and revealed that his mystical powers have been tapped into by Adolf Hitler in 1945, who used the ancient Spear of Destiny to link the fate of the Nordic gods' Ragnarok with that of the universe itself. Doctor Fate then transported the team to 1945 and then to Asgard where the Justice Society members were merged with the Nordic gods and thus changed the course of the Ragnarok. Unfortunately, just as the Justice Society prevailed, they found themselves locked in a perpetually-repeating battle from which they cannot escape, that they must repeat the battle to ensure the safety of the universe. Dr. Fate transported Power Girl and Star-Spangled Kid out of Asgard and back to the present time, then he himself was transported back to the present by the Spectre.
Several years later in our own time, the Spectre with the help of Waverider transported the Justice Society team out of Asgard to contend with the threat of the interdimensional demon called Abraxis. By having Abraxis's "daemen" take their place in the continuing Ragnarok cycle, Waverider brought the Justice Society members back home to the New Earth reality. Sadly, a few years after their return, some of the members would face death at the hands of Extant, who used his powers to remove the various spells that kept most of the team members healthy and active.
There were several key events which heralded the return of the Justice Society of America. The first took place during the final stages of the Zero Hour event. Moments before he was fated to die, Hourman was visited by his android descendant from the 853rd century. The android Hourman, who carried the genetic markers of the Tyler family line within his biosoftware, froze time long enough to show Rex Tyler a vision of the future. In his vision, he witnessed the reformation of the Justice Society of America, uniting seasoned veterans with aspiring hopefuls. He died content with the knowledge that the legacy of the JSA would live on. 
The second event centered around a fifteen-year-old boy named Jakeem Williams. A child of prophecy, Jakeem was born in the seventh hour, of the seventh day, in the seventh month of a year ending in the number seven. As such, Jakeem (or J.J.) inherited the power of the Bahdnesian Thunderbolt known as Yz; the same Thunderbolt that was bonded to Johnny Thunder decades past. A water sprite from the 5th Dimension known as Qwsp manipulated events causing two Genie Princes of the 5th Dimension, Yz and Lkz, to battle one another, using Earth as their battlefield. The JLA were the first to respond to the emergency, and they enlisted the aid of the Justice Society due to their past affiliation with the Thunderbolt. While the JLA (with the help of Captain Marvel) managed to halt the calamity, the Justice Society protected the streets of chaos-torn Keystone City. Two events of significance happened at this time. First, Sentinel managed to use the Green Flame of Life to free the Spectre from imprisonment in the Astral Boundary, and second, the Justice Society discovered that their longtime teammate, Wildcat, possessed the ability to return from the dead. Moments after suffering a fatal magic blast at the hands of Qwsp, Ted Grant rose from the ground as if nothing had happened. Like the cats of ancient myth, Ted literally possessed nine lives. Following this adventure, Jay Garrick took it upon himself to watch over J.J. Thunder to make sure that he harnessed the power of the Thunderbolt responsibly. 
The event that led to the official reformation of the Justice Society involved the death of one of their oldest members. Wesley Dodds, the original Sandman, had a dream which foresaw the birth of the next inheritor of the mantle of Doctor Fate. He knew that this child of destiny would bear the mark of the Ankh on his right arm, and that his very existence made him a target of great danger.
The sorcerer known as Mordru coveted supreme power, and engaged upon a bloody crusade to destroy the agents of order. On his journey, he slew several mystical agents, including Jared Stevens and Kid Eternity. He confronted Wesley Dodds on Mt. Kalaish in western Tibet, and attempted to wrest the knowledge of the child’s whereabouts from him. Throwing himself from the peak of the mountain, Dodds never gave up the identity of the Fate child. 
Sanderson Hawkins, the man once known as Sandy the Golden Boy, learned of Dodds's death through a dream, and knew that he had thus inherited his mentor's gift for prophetic dreaming. Surviving JSA members gathered at the Dodds estate to pay their respects, and the team committed themselves towards saving the Fate child.
The lineup consisted of seasoned heroes such as Sentinel, the Flash, Wonder Woman, and Wildcat, but also included younger legacy heroes such as Starman, Nuklon (now calling himself Atom Smasher), the Hourman android, a new Hawkgirl, and a new Star-Spangled Kid. Former JLA member Black Canary also joined the group in honor of her late mother.
The JSA scoured the globe in search of the child, and even worked alongside Golden Age adventurers such as the Scarab, Speed Saunders, and the ghost of Kent Nelson, the original Doctor Fate. Mordru summoned the undead Sons of Anubis to fight the heroes, but he could not prevent the Fate child from being born.
Hector Hall, late of Infinity, Inc., had died and been trapped in the other-dimensional world known as the Dreaming. His spirit reincarnated itself into an infant body, whereupon he mystically aged himself to adulthood so that he could wield the powers of Doctor Fate. After a dramatic battle with Mordru, Doctor Fate trapped the sorcerer inside the Amulet of Anubis.
With a new team assembled and ready for action, the only decisions left to be made were: who was to lead them, and where they would congregate. Sanderson Hawkins, now calling himself Sand, became the first chairman of the reborn Justice Society. One of his first initiatives as chairman was to establish a permanent base of operations. He hired architect John Stewart to refurbish Wesley Dodds's old family mansion in New York City. The JSA used the mansion as not only their new headquarters, but also as a museum commemorating the legacy of the brave men and women who helped to forge the Golden Age of heroes.
Following Infinite Crisis, the Justice Society was seen at their Metropolis Headquarters during Lex Luthor's Thanksgiving Parade, featuring Luthor's new Infinity, Inc. The "team" included Green Lantern, Wildcat, and the Flash. They later reunited with the younger team members (including the renegade Atom-Smasher) and went to Oolong Island to free Black Adam from captivity. The Justice Society sought to bring Adam to justice for the destruction of the sovereign nation of Bialya. While the JSA stood their ground against the Chinese team known as the Great Ten, Atom-Smasher helped to free Black Adam. 
The Justice Society formally reformed as an active group after the events of 52 with Power Girl as its chairperson. One of their first missions was trying to regulate the well-intended, but misguided, efforts of Gog, while also dealing with the personal problems of various members like Damage (whose face was ruined), Sandman (cannot dream), Citizen Steel (cannot feel anything),and their associates such as the Earth-22 Superman (personal failing) and Judomaster (criminal trial). Currently, the team is facing a potential split because certain members, like Magog, believe the team's methods are outdated.
The members -- all active, reserve and potential -- have grown to excessive numbers but are all appreciative as the successors to the legacy of greatest costumed heroes team of New Earth.
Equipment: None known.
Transportation: Throughout the years, the members of the Justice Society have employed various means of transportation. In many cases, members could be found flying inside of Wonder Woman's invisible robot plane. In other situations, Green Lantern would create a giant force-field bubble with his power ring and tow team members through the air as he flew. A few of the JSA members, such as the Spectre and the Flash could travel by way of their own unique powers. The JSA of the modern era, under the leadership of Sand, used a custom-designed hover-jet called the Steel Eagle. The Eagle was designed and built by JSA reserve member, Pat Dugan.
Weapons: Collectively, the JSA did not generally employ many weapons. Individual members however, were known to use various weapons and gadgets as part of their crime-fighting identity. Hawkman used a wide variety of ancient melee weapons. Sandman used a gas-gun to render opponents unconscious. Green Lantern owned a distinctive Green Lantern Ring. Doctor Mid-Nite carried a pack of Blackout Bombs. Starman and Stargirl used different variations of the Cosmic Rod, and Wonder Woman used a magical golden lasso to ensnare opponents.
The Justice Society of America is a team of great super heroes assembled by the President to fight in World War II, specifically against Hitler. Since then they've taken to training the new and immortalizing the old as they take their crime fighting to the streets as the JSA and JSA All-Stars. Find out more at: http://dc.wikia.com/wiki/Justice_Society_of_America