In May 1965, Humanity became painfully aware of one alien species: the Qularr, a quasi-insectoid, quasi-crustaceanoid species from an unknown planet. Approaching under the concealment of stealth fields, the Qularr scouted Earth in search of the right place to land.
The Qularr found what they were looking for in a small, unnamed barrier reef island about a hundred miles off the coast of Japan. At the time it was unclear why they chose that location. Decades later the revelation of potential Lemurian and Elder Worm artifacts in that area makes scholars wonder if there were more to the choice than tactical benefit. Using their alien technology the Qularr raised part of the seabed, turning the atoll into a large, single island with an active volcano at the center.
With their forward base complete, the Qularr landed and released their cargo: dozens of gigantic monsters captured on alien worlds or bred with Qularr bioengineering. Humanity learned it was under attack when Qularr transports disgorged their weapons onto the first major targets, in Japan. The robotic "dinosaur" Mega-Terak attacked Tokyo, while his flesh-and-blood "brother" Cazulon was sent to Kobe. But the land of the Rising Sun wasn't the only victim of Qularr aggression. New York City was attacked by two creatures, the gigantic "bird-demon" Pazuron and the "lizard-cat" Velzara. The winged serpent Ganika was turned loose on Chicago, while the three-headed "dragon" Mitsura ravaged the Los Angeles area. A gargantuan, fire-breathing, radioactive gorilla-like beast called Qwyjibo smashed through London, and across the Channel the toad-like Doku slaughtered thousands of Parisians with his poisonous breath. The "atomic mutant lizard" Zorgatha lay waste to Beijing, and the lightning-firing "eagle" Vakulon assaulted Moscow.
The initial Qularr attacks succeeded, but Earth's superheroes were often able to slow down the monsters just long enough for heavy force to arrive before a city was totally destroyed. In New York the combined might of the Sentinels, the Justice Squadron, and the Fabulous Five, plus several Army battalions, was enough to halt Velzara's and Pazuron's rampages, and then to destroy the monsters. But in other cities the monsters weren't slain, merely knocked unconscious or driven away.
With their initial attack blunted, the Qularr switched to more conventional tactics, hoping to win the day with superior technology, but there were just too few of them. Human soldiers, aided by dozens of superheroes, pushed Qularr forces back toward the island. By mid-June, the Qularr apparently decided they'd had enough: they returned to their island, boarded their ships, and departed Earth. They left behind the surviving monsters.