In 1999, Mark Waid and Alex Ross released what would go down as one of history's greatest comic book stories in Kingdom Come. One of the story's most important messages is the importance that superhero ethics has in the world of comic books and what it means to be a hero.

While comics have a habit of releasing exceptional storylines with important messages, few come even close to matching Kingdom Come's importance. The likes of Watchmen, The Dark Knight Returns, Kraven's Last Hunt, and Batman: The Cult have gone down in legend, but the seminal series by Waid and Ross has both a timeless and unique message.

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The story focuses on a world set a generation into the future, where the original Justice League have disbanded and gone their own way. While a disabled Batman now defends Gotham's streets with use of mech-suit Batman drones, Superman has retired and retreated into solitude away from civilization. The beginning of the story poses the question of why Superman abandoned the world to the excesses of the younger generation of metahumans.

As the world is ravaged by an ongoing war between those young metahumans, with some claiming to be heroes battling those they deem villains, regular people are left helpless to watch as the world is caught in the crossfire. The new and young being known as Magog leads a ragtag group of so-called heroes as they make up the closest thing the world has left to a superhero team. But even Magog's team are reckless, destructive, and ignorant of the impact of his war on regular people.

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However, when a tragedy strikes, Superman heeds the call from Wonder Woman to come out of retirement for the betterment of the world. With Magog sent away into hiding, Superman begins to approach heroes, both old and new, with an offer to reform the Justice League and restore order. The destruction and near anarchic values of the younger heroes forces Superman into an out-of-character decision - in order to police his own, he imprisons the unruly heroes. The story covers how when the ethical heroes abandon their role as a leader, something far worse fills that void.

Kingdom Come's depiction of the brash and unchecked younger heroes' recklessness and how without responsibility, power can become destructive is also a reminder of the famous Spider-Man code. The rapid devolution and anarchy that took place in the absence of Superman and Batman's well known "no killing" code showed readers why there are lines that superheroes should never cross. With many casual fans questioning why Batman doesn't simply kill Joker or why Superman doesn't kill Lex Luthor, this series serves as an excellent answer to those questions. Once superheroes turn themselves into judges, juries and executioners, they immediately risk becoming destructive tyrants.

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By illustrating a world left to the younger and aimless generation of heroes and villains, the story showed the importance not only of the moral code of the older heroes but also their mentorship. The return of the older heroes, along with their code, returns order and hope to the world and its people. In many ways, the story was a subtle rebuke of that era's fixation with 'edgy' heroes, and fans who began to ask why Batman would leave someone as evil as Joker alive. It also showed readers how when a hero abdicates their responsibility and code, it can push even the best of them to their limits.

While many stories over the years, both before and after, have sought to explain this code, none have come close to Kingdom Come. The story serves as a long and deeper exploration of the meaning behind the infamous line "with great power comes great responsibility." Any fan who wants to understand the meaning of the superhero code, and why heroes have the restraint they do, should begin with this iconic story. The story here is simple - when the powerful don't have a code, the powerless are the ones who pay the price.