The Global Guardians is a team of international superheroes belonging to DC Comics. It was created to feature the heroes from the DC Universe that hail from places besides the United States, although its role (and many of its members) were taken over by the Justice League International team.
(Should not to be confused with the group of the same name from the Invincible comicbook, which this group precedes.)
The characters are older than the team itself. They were first introduced in issues #7-9 of the Superfriends comic book in the late 1970s. In that multi-part story, two young aliens, Zan and Jayna, (in their first comic book appearance) came to Earth to warn that Grax, an alien villain, had planted bombs on Earth's six continents to destroy the planet in revenge for being thwarted by Superman. The Justice League of America then scatters around the globe to find them, and are helped by the heroes of the various countries where they are hidden to penetrate their defenses and disarm them. In the end, however, it is the League's kid sidekicks, Wendy and Marvin, who find and beat Grax himself—and then announce that they are retiring, conveniently allowing the Wonder Twins to replace them (which happened offscreen in the TV show.)
The characters then appeared sporadically in the Super Friends comic (which explicitly was not part of the main DC Universe) but not as a team. Two of them—the Seraph (of Israel) and Jack O'Lantern (of Ireland)—even starred in their own adventures in a few backup stories.
The team itself was formed in DC Comics Presents #46 (June, 1982) in order to introduce them officially into continuity. In that story, the ancient African sorcerer Doctor Mist gathered the heroes (and Superman) to stop another, evil sorcerer's plan, and then announced they were a team to be called when he decided it was needed.
After DC's big reboot in 1985, the team was reinvented as having been organized instead by an organization called The Dome, with authorization from the United Nations. But when DC decided to reinvent the Justice League as an international team, they had the Guardians disbanded (for no good reason) and their status transferred to the League. Some former Guardians joined the team, most notably Fire And Ice. Others, such as Jack O'Lantern, were actually used as villains! (They had been brainwashed.)
The various members of the Guardians have appeared sporadically since then. Dr. Mist and Jack O'Lantern co-starred in the (short lived) series Primal Force about a team of supernatural heroes. Others were killed off to set up some villains as being really dangerous. Grant Morrison brought back some of the former members during his JLA run to join a team of (former) American super soldiers called the Ultramarine Corps who set themselves up as an international peacekeeping force (basically bringing back the concept of the Global Guardians as separate from the JLI to the DCU). They were seen in several Justice League related specials, operating out of the floating city of Superbia, up until Final Crisis.
(Note that various international heroes have been introduced by DC Comics over the years but not all have been Guardians.)
Now that the DC Universe has been rebooted (again) the history of the Guardians, if they ever existed as a team, remains to be seen. Some of them can be seen in the new Justice League International series.
The ending of Doomsday Clock has mention of Wonder Woman working alongside the United Nations to reform the Global Guardians after multiple international super teams almost destroyed Metropolis following Superman and Firestorm being framed for committing mass murder in Russia. Each of the different super teams intend to nominate one of their members to act as their representatives in the new Global Guardians.
More detailed information here: 
- Doctor Mist: Nommo of Africa. Homo Magi sorcerer; later founded Primal Force. Killed by mystical forces, appeared alive again and was then tossed in a vat of acid by the sorcerer Mordru, but is alive again due to Flashpoint and now part of Justice League Dark.
- Little Mermaid: Ulla Paske of Denmark (actually a mutant from Atlantis). Swims, flies, breathes water, and can turn her legs into a fishtail. Killed in battle with the Queen Bee, then popped up alive again. When Flash questioned her on this, she informed him that it had been an evil clone.
- Jack O'Lantern: Daniel Cormac of Ireland. Wields a magic fairy lantern that acts similar to a night-themed Green Lantern Ring: flight, flame projection, teleportation, illusion casting, enhanced strength, and the ability to create fogs. Killed by Queen Bee, replaced by the evil Marvin Noronsa, found alive, killed again by 'natural causes', and replaced by:
- Jack O'Lantern: Liam McHugh of Ireland. Self-proclaimed freedom fighter, joined Primal Force and the Ultramarine Corps.
- Owlwoman: Wenonah Littlebird of the USA. Flight, enhanced senses, tracking skills, and retractable claws. A Cherokee. Her descendant was seen on the JLA of the 853rd Century.
- Rising Sun: Izumi Yasunari of Japan. Flight and fire generation and control. Later a member of "Big Science Action". Has not died yet, but was shown as a mind-controlled aging alcoholic fighting the Super Young Team.
- Tasmanian Devil: Hugh Dawkins of Australia. Super-strength, claws and fangs. Also, he's gay. Later joined Justice League International, and the Ultramarine Corps. Killed and skinned by Prometheus in Justice League: Cry for Justice, but returned to life in a Lazarus Pit.
- Seraph: Chaim Lavon of Israel. Wields the ring of Solomon, the mantle of Elijah, the staff of Moses, and the hair of Samson, granting him wisdom, teleportation, invulnerability, water manipulation, and super-strength. He's Jewish.
- Tuatara: Jeremy Wakefield of New Zealand. Can see the future with his third eye. Has a fin on his head. Left in a coma by Fain Y'Onia. Named after a three-eyed lizard.
- Thunderlord: Liang Xih-k'ai of Taiwan. His voice creates various sonic effects, including sonic blasts, mind-control, and perfect mimicry. He's a Buddhist. Killed by Fain Y'Onia, but made a cameo in The O.M.A.C. Project despite being dead.
- Olympian: Aristides Demetrios of Greece. Wears the Golden Fleece, granting him the powers of the Argonauts, including (but not limited to) strength, precognition, telescopic and x-ray vision, speed, wisdom, walking on water, flight, shapeshifting, and invulnerability. Possibly schizophrenic. Later joined the Ultramarine Corps and dated Wonder Girl's mother.
- Godiva: Dorcas Leigh of England. Has Prehensile Hair. Lost her powers in battle with Fain Y'Onia, and was later scalped by Delores Winters. In the "New 52" reboot, has joined the Justice League International.
- Impala: M'Bulaze of South Africa. Super-speed and leaping. He's a Zulu. Crippled by Fain Y'Onia, and later killed off-panel in Roulette's game house. Succeeded by Kid Impala, who joined the Ultramarine Corps.
- Wild Huntsman: Albrecht Von Mannheim of Germany. Reincarnation of an ancient warrior; has enhanced strength and tracking skills. Also has a horse and dog. Disappeared while fighting Fain Y'Onia into the mists of time, but later appeared in Red Robin acting as security for potentially dangerous museum artifacts in Germany.
- Bushmaster: Bernal Rojas of Venezuela. A Batman with a reptile theme. Throws snakes at people. Killed by a bank robber after being blinded by Fain Y'Onia. Possibly replaced by someone else, as someone in his costume cameoed with the Ultramarine Corps.
- Green Fury: Beatriz Da Costa of Brazil. Controlled magic fire that could burn or freeze, create illusions, and allowed her to fly. Retconned into:
- Fire aka Green Flame: Beatriz Da Costa of Brazil. Breathes fire; later could sheath herself in flames, fly and throw fire blasts. She's a supermodel and a spy. Changed her hero name to Fire when she teamed up with Ice. Later joined the Justice League International, creating a solid career for herself. Has appeared in the Justice League of America TV pilot, Justice League Unlimited, and Batman: The Brave and the Bold.
- Icemaiden: Sigrid Nansen of Norway. Controls ice and cold in various ways. Bisexual. Later joined the Justice League of America. Had her skin removed by Dolores Winters, while still alive.
- Ice aka Icemaiden II: Tora Olafsdotter of Norway. Generates and controls ice and cold. Princess of a secret race of ice people, she replaced Sigrid as Icemaiden (at her request) before teaming up with Fire. Sensitive and caring, has defeated powerful villains simply by offering a sympathetic ear. Later joined the Justice League International, ensuring her a long career. Killed by The Overmaster; brought back by Russian villain Kerimov. She, alongside Fire, has shown up in Justice League and Batman: The Brave and the Bold.
- Centrix of Canada, Chrysalis of France, Cascade of Indonesia, Templar Knight of France, and Tundra of Russia: Joined and disappeared into obscurity between appearances of the team. Templar Knight even died off-panel.
- Fleur-de-lis of France: Badass female spy. Later joined the Ultramarine Corps.
Tropes related to the Global Guardians:
- America Saves the Day: Originally subverted, then applied when the Justice League, an American team, took over the Guardian's role.
- Back from the Dead: When the Global Guardians made their return in Green Lantern following Infinite Crisis its return included some of the The New Guardians, who had been killed off years ago. Some of these members were then killed by Prometheus in Justice League: Cry for Justice.
- Canon Discontinuity: All the heroes' appearances up until the team-up with Superman.
- Captain Ethnic: Some of the Guardians have been accused of being this. In reality, they were no worse than any other heroes (except for being reduced to cannon fodder.)
- None of the TV show's international heroes (Black Vulcan, Samurai, Apache Chief and El Dorado) ever appeared in the comics.
- C-List Fodder: Unfortunately, this is what the team has been reduced to in recent years.
- Flying Firepower: Fire, a Brazilian woman who has green Wreathed in Flames and flies around. Later joined the Justice League International, creating a solid career for herself.
- Heroes "R" Us: The Dome existed to provide help to heroes that needed to cross international boundaries (not just the Guardians.)
- The Mole: Chrysalis. Word of God states she was designed by an antisemitic robotics specialist to ethnically cleanse France by seeming innocent then releasing disease-carrying butterflies. Her creator died, but she's still operating under her original programming.
- Multiarmed And Dangerous: Grax had four arms (and blue skin.)
- Multinational Team: Note they did have one American member, the Native American Owlwoman.
- Plot Tailored to the Party: The heroes' introduction suffered badly from this. Every one of Grax's bombs had defenses that conveniently could only be penetrated by a particular Guardian's powers. Obviously the idea was to give the new heroes a chance to show off, but it could have been done more logically.
- The Power of Rock: Thunderbolt often sings various songs by various musical artists. "Justice League International Quarterly" had the Guardians (then in Biyala after Queen Bee's fall) face against the "Hero Group" based in Lower Pluxia. Thunderbolt faced the Desensitizer, a female who could prevent his vocal sonic blasts just by thought, leaving him gasping for air. Focusing his will (and his song) into his voice, he broke into "I Am, I Said" by Neil Diamond, which made Desensitizer swoon (she adored Neil Diamond).
- Public Domain Location: Doctor Mist was the first king of Kor, subsequently ruled by Asheya, the title character of She.
- Really 700 Years Old: Doctor Mist, who is from an ancient African civilization.
- Time Bomb: Grax's plan. Note that the heroes almost missed one, because it was hidden in Earth's sixth, uninhabited continent... Antarctica.
- Unexplained Recovery: Little Mermaid was originally killed by the impostor Jack O'Lantern. When she reappeared in Justice League Europe, she handwaved her death by saying to Flash that he was thinking of her Evil Twin.