When the Justice Society of America met for the first time, that was an event that then-nascent comic book world had never experienced before. Comic book characters from two different imprints meeting together for the first time ever. It was a momentous occasion, and it is one that DC would later replicate two decades later when the Justice Society of America met the Justice League of America in the first of many "Crisis" events in DC Comics history.

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There have been many major events since then, and here, we'll count down the 15 greatest DC Comics events of all-time. For the purpose of this list, an "event" has to be some sort of crossover, even if it is just a crossover between all of the "Batman" titles or all of the "Green Lantern" titles.

15 FLASHPOINT

Flashpoint cover

In 2011, the DC Universe was turned on its head and initially it was all caused by "Flashpoint." The concept behind the series is that Barry Allen decided that he could no longer live with the events that he discovered during "Flash: Rebirth," that the Reverse-Flash had gone back in time and killed Barry's mother and framed Barry's father for the murder. Originally, Barry's parents had a long, happy life. Now, Barry grew up an orphan with a father accused of murdering his wife, so he went back in time and stopped the Reverse-Flash. However, the end result was that he drastically altered the timeline of the DC Universe, which was shown in "Flashpoint" by Geoff Johns, Andy Kubert and Sandra Hope.

In this new timeline, the Justice League never formed, the Amazons and Atlanteans were at war with each other and Batman was Thomas Wayne, whose son Bruce had been murdered years earlier. Ultimately, when Barry convinced everyone that this was not how things were meant to be, he was aided in his attempts to go back in time once more and let things go as they were. However, when Barry returned to the "present," the DC Universe had been radically changed again, which was the "New 52." We are only just now learning that there might be something more to it than simply Barry messing with time.

14 ZERO HOUR

Parallax looms over DC's heroes

Nearly a decade after "Crisis on Infinite Earths," the ragged edges of the DC Universe's timeline were beginning to show a little bit. Things were not falling apart, of course, but there were slight issues with time, including the fact that the Justice Society of America were around while it was becoming increasingly unrealistic to have a bunch of heroes from World War II running around the DC Universe. "Zero Hour" (by Dan Jurgens and Jerry Ordway) dealt with these problems.

Enter Hal Jordan, who was in his Parallax days. Hal believed that he could recreate time, only he would make things better this time, such as making sure that Coast City was never destroyed (and if it was never destroyed, then he would have never have destroyed the Green Lantern Corps afterwards). Various characters from alternate timelines also began to pop up, like a Barbara Gordon who was still Batgirl when she was currently in her Oracle days. Ultimately, the DC Universe was restarted the same as it was before, only every writer was given the chance to fix any nagging continuity issue that they felt like (such as the "Batman" titles making it so that Batman never found his parents' murderer).

13 INVASION!

In 1962, inspired by Wallace Wood's brilliant work for EC Comics, Topps Comics released a series of cards called "Mars Attacks," penciled by the great Wood (and then finished by Bob Powell and painted by Norman Saunders). It told the story of an alien invasion of Earth by Martians and it absolutely captured the imaginations of an entire generation of young readers. Nearly three decades later, those creators were writing comics, and writers Keith Giffen and Bill Mantlo (in his first DC Comics project) decided to bring that feeling over to the DC Universe.

A group of alien races, led by the Dominators, determined that Earth was too dangerous, so they decided to invade it to take control of the planet before it could threaten them all. Earth's superheroes teamed up, led by Captain Atom and Wonder Woman, and fought off the Invasion in the main "Invasion!" series by Giffen and Mantlo, with art by Todd McFarlane and Bart Sears. As the aliens were driven off, they set off a "gene bomb" that nearly killed any person on Earth with metahuman powers.

12 IDENTITY CRISIS

DC's Identity Crisis raped and killed Sue Dibny, Elongated Man's wife

Brad Meltzer, Rags Morales and Michael Bair combined for "Identity Crisis," a look at the darker side of the DC Universe. Elongated Man's beloved wife, Sue Dibny, was found murdered in their home, burned to death. At her funeral, a group of veteran Justice League members got together and believed that it had to be the work of Doctor Light. They now revealed that years earlier, Doctor Light had broken into the Justice League's satellite and raped Sue, who was alone on monitor duty. When the League captured Doctor Light, a select group of the League (including Green Arrow, Hawkman, Flash, Black Canary and Zatanna) decided to essentially lobotomize him. They then messed with the minds of a few other villains, all courtesy of magic spells by Zatanna. When Batman discovered what they were doing, they erased his memory of the events, as well.

When Doctor Light turned out to not be the killer, it seemed like the entirety of the DC Universe was at risk, as someone who knew their secret identities were striking at heroes. In the end, it turned out that the killer was Jean Loring, the ex-wife of the Atom, who wanted to cause problems so that the Atom would bring her back into her life for her "protection" and they would get back together.

11 LEGENDS

Following "Crisis on Infinite Earths," the DC Universe was greatly altered, although it was a bit unclear how everything fit together in a new continuity where certain heroes were only now being introduced into the DC Universe (despite traditionally being classic heroes in the comics). The miniseries "Legends," by Len Wein, John Ostrander, John Byrne and Karl Kesel brought the heroes of the DC Universe together again for the first time. Wonder Woman, for instance, was only now meeting everyone and Captain Marvel was newly integrated into the DC Universe.

The heroes were drawn together by a plot by Darkseid's operatives to turn the world against its superheroes. This distrust helped lead to the creation of the Suicide Squad by Amanda Waller (one of the major spinoffs of "Legends"). In the end, the heroes all teamed up and stood up against Darkseid's flunky, Glorious Godfrey, and a new Justice League rose out of the ashes.

10 INFINITE CRISIS

Earth-2 Superman looms over DC's Infinite Crisis

At the end of "Crisis on Infinite Earths," there were a few characters who seemed as though they might have survived the creation of a singular DC Earth out of the Multiverse. In "Infinite Crisis" (by Geoff Johns, Phil Jimenez and Andy Lanning), those characters came back into the DC Universe. However, in the time that they'd been away, they had been monitoring things and Alexander Luthor and Superboy Prime have been twisted into being filled with hatred for this Earth, feeling as though the heroes of DC had wasted the blank slate that they had given them, as they felt as though things were far grimmer and grittier than they should have been.

The original Superman (and his wife, Lois Lane), were convinced that the new heroes were a problem, but over time, they realized that Luthor and Superboy Prime had gone mad, as Luthor's plan was basically to just wipe everything out entirely. In the end, the heroes stopped the insane plot of Luthor, but in the process, also revealed that there was no longer just one Earth! The Multiverse was back!

9 DC ONE MILLION

The Justice Legion A travelling back in time

In one of the greatest feats of coordination known to superhero crossover history, "DC One Million" featured a main miniseries written by Grant Morrison and drawn by Val Semeiks, plus Morrison helped to coordinate the plots of almost every other one-shot that tied into the crossover event! The concept of "DC One Million" was that the Justice League was visited by the Justice Legion from the 853rd century, as that is the year where "Action Comics" would hit #1,000,000 if the series continued to publish on a monthly schedule.

Superman-Prime was about to show up again for the first time in centuries and the Justice Legion wanted their original inspiration, the Justice League, to be there to see it. Therefore, they came back to take the Justice League into the future while they stayed behind in the "past" to watch things for the Justice League. Of course, there was a villainous plot that threw things for a loop, as Vandal Savage (who was alive in the present and the future) and the rogue sun known as Solaris, were causing problems both in the present and in the future. The one-shots showed either the various other heroes of the future or the adventures of the modern Leaguers while visiting the future.

8 THE DEATH OF SUPERMAN

Superman's cape waving like a flag from The Death of Superman

In 1992, in response to their inability to do their original story (which was to have Lois Lane and Clark Kent get married) due to conflicts with the then-upcoming "Lois and Clark: The New Adventures of Superman," the writers of the various "Superman" titles (Dan Jurgens, Louise Simonson, Jerry Ordway and Roger Stern) decided to instead just kill off the Big Blue Boy Scout. The way they pulled this off was to introduce a new character, an almost unthinking monster whose only purpose was to destroy things. Dubbed "Doomsday," he cut a swath of destruction towards Metropolis.

The Justice League couldn't handle him, so it came down to just Superman. In a fascinating storytelling approach, the artists for the event (Dan Jurgens, Jon Bogdanove, Tom Grummett, Jackson Guice, Brett Breeding, Dennis Janke, Doug Hazlewood and Denis Rodier) had increasingly larger panels as the story went on. So it went from four panels per page to three panels per page to two panels per page until the final issue, with the actual death of Superman, was all full-page splashes by Jurgens and Breeding.

7 KNIGHTFALL

Directly following the success of "The Death of Superman," DC Comics launched a similar event for the "Batman" line of comics that sprung out of stories introduced a year earlier. In "Batman: Sword of Azrael," we met a young man named Jean-Paul Valley, who was brainwashed into becoming an assassin called Azrael. He broke free of the programming and began to train as a hero under Batman and Robin. Meanwhile, a new villain came to Gotham City, Bane, who was both brilliant and really strong due to the powerful Venom coursing through his veins.

Bane orchestrated a breakout of Arkham Asylum, forcing Batman to hunt down all of his most famous villains. Once he finished this task, the exhausted Batman was then taken on by Bane and had his back broken by the villain. Jean-Paul had to step up and take over as Batman, although his mind was not yet ready, and becoming Batman caused something to snap within himself, allowing him to defeat Bane but become a much darker version of Batman.

6 FINAL CRISIS

DC's Superman holding Batman's skeletal body, from the cover of Final Crisis.

For years, Darkseid had been trying desperately to find the Anti-Life Equation, which would give him power over Earth as a whole. He never did. In Grant Morrison, JG Jones and Doug Mahnke's "Final Crisis," though, he finally broke through and succeeded in his plan to conquer the planet. First, the New Gods were killed off one by one, including Darkseid's own son, Orion. While investigating Orion's murder, Batman was captured and was cloned by Darkseid's men in an attempt to create an army of Batmen.

Meanwhile, Darkseid's attack came through time itself, and it weakened the fabric of space-time enough that a rogue Monitor escaped and began to prey on the Multiverse as a whole. Superman encountered him while searching for a way to cure Lois Lane after she was injured in an attack. The heroes of Earth managed to fight back against Darkseid and take Earth back. Batman, meanwhile, escaped as well, and managed to kill Darkseid, but not before Darkseid seemingly killed him, as well (it was actually one of the dead clones of Batman). Superman and the rest of the heroes then helped defeat the threat of the rogue Monitor, which opened up access to the rest of the Multiverse following their introduction in "Infinite Crisis."

5 MULTIVERSITY

Following the proper re-establishment of the Multiverse at the end of "Final Crisis," Grant Morrison returned to the concepts of the Multiverse in his epic event, "Multiversity," which was delayed for years following the fact that "Final Crisis" Was so soon followed by "The New 52," which threw a bit of a wrench into the original plans that Morrison had. The crossover dealt with the introduction of the villainous Gentry, who were drawn to the DC Multiverse by the broken dreams of the various characters of the various DC worlds. The Gentry want to take control of independent though in general.

The crossover was brilliant framed as a series of one-shots, where each one-shot was a specific Earth in the Multiverse, and they each have to deal with the invasion by the Gentry, while connecting to each other only as fictional characters (like how Jay Garrick was a fictional character to Barry Allen before he met him in the classic "Flash of Two Worlds" story that established the DC Multiverse), so the characters would, in effect, be following along with the story as it went along. Morrison and the all-star cast of artists he worked for introduced great individual stories, as well as a striking overall crossover event that made the Multiverse seem like it would be so much fun to play with for future creators.

4 BLACKEST NIGHT

Green Lantern Vs. Resurrected Dead Heroes And Villains During Blackest Night

"Blackest Night," by Geoff Johns, Ivan Reis and Oclair Albert, was the culmination of a series of "Green Lantern" storylines that had introduced Yellow Lanterns, Red Lanterns, Blue Lanterns, Violet Lanterns and Indigo Lanterns to the DC Universe. In this event, we also met Black Lanterns for the first time. Black Lantern Rings showed up on Earth and began reanimating the corpses of pretty much every dead superhero and supervillain on the planet essentially as zombis and turned them on Earth's heroes.

The series helped to address the strange way that death is handled in superhero comics. Superheroes had been dying and coming back for years at this point and, now in this series, there was a sort of explanation for how this went on, and the event itself was sort of a response to it happening too many times. By the end of the series, a number of dead heroes and villains were returned to the land of the living.

3 BATMAN R.I.P.

Batman from the cover of DC Comics' Batman R.I.P.

Grant Morrison's long run on "Batman" was split into three distinct "Acts." The first act came to a conclusion in "R.I.P," which also included the classic Paul Dini/Dustin Nguyen/Derek Fridolfs tie-in story, "Heart of Hush, with Hush returning to haunt Batman in a big way by literally stealing Catwoman's heart! Once Batman resolved that mess, he had to deal with the increasingly aggressive actions of the mysterious secret society known as the Black Glove. The Black Glove had infiltrated Gotham City's elite for years. They now tried to take down Batman and they used an interesting approach - try to attack Batman's very sanity!

It seemed as though they succeeded, and Batman had snapped. However, the main message of this series was "Here's the thing about Batman. Batman thinks of everything." Batman had even prepared for a scenario where he might be mentally incapacitated, so he created a sort of altered personality that would take over to protect him. Once he returned to normal, he took down the Black Glove. However, after doing so, he headed off to "Final Crisis," where he seemingly "died," setting up Act 2, where Dick Grayson took over as Batman (Act 3 was when Bruce Wayne returned and formed Batman Incorporated to stop the evil group known as Leviathan).

2 SINESTRO CORPS WAR

DC Comics' The Sinestro Corps War, featuring Hal Jordan, Kyle Rayner, and Sinestro in combat poses.

As soon as he introduced the concept of the fear entity, Parallax, in "Green Lantern: Rebirth," and especially when he not only brought Sinestro back but had him work alongside Parallax, Geoff Johns had been working towards a bigger story. That story was revealed in "The Sinestro Corps War," where Sinestro revealed that, through the help of Parallax, that he had created his own rival group to fight against the Green Lantern Corps. Where the Green Lanterns were chosen by their willpower and ability to stand up against fear, the Sinestro Corps members were chosen by how good they were at instilling fear in others (yes, they did try to recruit Batman).

After Parallax took a turn possessing Kyle Rayner, as well, the Green Lantern Corps came together to take out the Sinestro Corps, but in the process, they had to break some of the major Green Lantern Corps codes, including the "no killing" rule, and the relaxation of those rules would eventually lead to trouble down the road. At the end of the story, Sinestro was shocked to learn that the people of Earth were able to be brave to not fear his Sinestro Corps enough to give Kyle a big boost in the final battle against the Green Lantern Corps at Coast City.

1 CRISIS ON INFINITE EARTHS

As noted earlier, the DC Multiverse had been introduced in the early 1960s, and from that point on, the standard in the DC Universe was that there were multiple Earths, with each Earth having its own distinct heroes. This allowed DC to add various new heroes from other publishers over the years, as those heroes would just get their own Earth so that they could be distinct from the rest of the DC Universe while still interacting when necessary. However, as the comic book market changed in the 1980s and Marvel became a dominant force in the industry, former Marvel creators Marv Wolfman and George Perez, who had already had great success using a more "Marvel" approach on "New Teen Titans," decided to re-invent the DC Universe by merging all of the various Earths into just one.

In order to do so, they wrote and drew (with inkers Dick Giordano and Jerry Ordway) the year-long "Crisis on Infinite Earths," where the various heroes of the Multiverse had to come together to prevent all of their worlds from being destroyed. Along the way, heroes fell in battle, as in a lot of cases, certain heroes were going to be written as not being part of continuity anyways (like how Superman was soon going to be the sole survivor of Krypton, so Supergirl was expendable) while others, like Barry Allen, still had their deaths remembered by the rest of the world. This was the crossover that defined all crossover events to come. That it also managed to be an interesting story on its own is nothing short of magical.

What is your all-time favorite DC Comics event? Let us know in the comments section!