Even for a hero as powerful as Superman, it helps to have friends in equally high places. Over the years, the Man of Steel has had several allies in his corner of the DC Universe, many of whom make up his "Superman Family." This has briefly resulted in one of the biggest missed opportunities in DC Comics.
At various points in the post-Crisis on Infinite Earths continuity, the Last Son of Krypton has formed a national team called the Supermen of America. This "Justice League" of Superman allies has had two incarnations, neither of which ever took off. Given the timing of the second version of the team, this was perhaps Superman's biggest creative loss yet.
DC Introduced the Supermen of America Team - Twice
The first version of the Supermen of America was created by Stuart Immonen and debuted in a special one-shot in 1999. The team was funded by Lex Luthor to act in Superman's absence whenever he was away. Their leader was Outburst, who had once been saved by Superman during Doomsday's rampage in Metropolis. Despite the name, none of them had any real connection to Superman, lacking even a similar power set or costumes. They never made much of a splash, with most of the team being unceremoniously killed off during the events of the Infinite Crisis.
The second version of the Supermen of America debuted in 2011's Superman #714 (by J Michael Straczynski, Chris Roberson, and Jamal Igle) which was one of the final comic book issues to release before DC's continuity-changing New 52 reboot. The issue capped off the controversial "Grounded" storyline, in which Superman walked across America in order to reconnect to the people who had pledged to protect. The conclusion of the story was a rededication to that mission, but also a realization that, for as much as the world needed Superman, he couldn't be everywhere at once. Thus, he formed a new Supermen of America with some familiar faces.
Superman Family members Conner Kent/Superboy, Supergirl and Steel joined the team, along with a reformed version of the villainous Livewire and Iron Munro. Munro was a member of the forgotten Young All-Stars, with his place in continuity being used to slot him in for Golden Age Superman. Unfortunately, the team was never seen in action together, as that continuity promptly ended right after their introduction. Given how much the New 52 changed, it was impossible to simply pick up the pieces as if everything was the same.
The Supermen of America Team Has Been Consistently Doomed
As far as the original Supermen of America went, the team never had much of a chance at long-term success. They thematically had very little to do with Superman himself, which was a problem that already plagued the non-Kryptonian versions of Supergirl. Thus, it's no surprise that they were quickly done away with given their minute importance. Superman himself seems to barely remember the team, and it's possible that Infinite Crisis and/or Final Crisis erased them from continuity anyway.
As for the version that appeared right before the New 52, it was likewise dead on arrival. As mentioned, continuity would promptly be rewritten from the ground up, with the Superman Family fractured and Golden Age comic book characters such as Iron Munro erased. It didn't help that this incarnation came about after "Grounded," a storyline that was far more controversial than actually good. This probably gave an unnecessarily negative aura to what could have been an incredible concept, as the Supermen of America would have allowed Superman's mythos to flourish in much the same way as Batman's has.
Being associated with "Grounded" is probably why, even with the Superman Family restored in the post-Rebirth timeline, the Supermen of America have remained untouched. Ironically, it was the first version of the team that got a somewhat cynical revamp in the hit series Superman and Lois, with the army using a force of humans that were given Kryptonian-like powers to exclusively protect America in a way that Superman wouldn't. Since this was perhaps the team's biggest push, it's likely that the Supermen of America will remain an aspect of the character's mythos that's mostly unrealized.