Gaia's Uprising

Gaia's Uprising was an armed conflict that encompassed the entirety of the Greek Mythological world, with nearly all divinities and mortals participating in some form. Led by Gaia, entire armies of long-thought dead monsters attack Mount Olympus, the Overworld, and the Underworld simultaneously, with the former being the largest group so they could free those within Tartaros.

Prelude
Gaia, the Primordial Mother Goddess of the Earth, has had a sordid history with those who held the role of Chief Greek God. The Mother Goddess' first betrayal began with her husband Uranus, whom she spurred Cronus to castrate after his imprisoning of her other children. When Cronus placed the Cyclopes and Hecatonchires back into Tartaros despite their assistance, Zeus was saved from Cronus by Gaia and Rhea, who later waged the Titanomachy against his father and imprisoning him in Tartaros. Zeus' turn would came after the death of the Gigantes, when Gaia birthed the monster Typhon and sent it against Zeus and Olympus, only for it to be imprisoned as well.

Knowing that she would simply try again, Zeus stole much of Gaia's power in an effort to prevent any more attempts on his throne. Gaia became an empty shell of her former self without her ability to create, preferring to live within seclusion on Earth, rather than the Greek World. Within her state of depression, Gaia was located by the Fallen Angel and King of the Infernal Hells Lucifer, who offered her a method of retribution in the form of the Enduring Womb against the Olympians.

Returning to Olympus, Gaia began recruiting disloyal servants to the current regime and having her agents collecting the souls of the long dead.

Mount Olympus
Taking on an aggressive strategy, Gaia and her opposition forces attacked Mount Olympus with creatures capable of flying on their own, or can scale the mountain side. Fighting quickly spread throughout the mountain passes as the Rebel's ground forces were carried by airborne creatures onto the mountain, slowly pushing the Olympian forces up the paths and towards the peak. Chaos Titans battled their Olympian counterparts in devastating battles that would leave any mortal as a ashen-blood pool.

When the war reached the Olympian Peaks, Zeus and Gaia engaged in a war of attrition against one another and their forces. Other members of the Twelve Olympians fought against the invaders as well, namely Apollo and Artemis who sniped great numbers on their own, Dionysus who led his Satyr into the fray, and Hermes who engaged in hit-and-run attacks. Lasting for nearly a week, the numbers of both sides slowly dwindled until it was only the strongest to remain, with the Olympians forcing Gaia into submission and later imprisoning her into Tartaros after the end of the rebellion.

Overworld
On the Overworld, Gaia's forces invaded human territory and the Seas, only stopping to do battle against any who resisted. Divided in two theatres, the Olympians Ares and Athena worked together to lead their human and supernatural allies into battle and being supported by the Automatons of Hephaestus which he began mass producing. In the seas, Poseidon was challenged by legions of aquatic monsters, including copies of the hydra and feral creatures that willingly joined Gaia.

With the combined might of both Gods of War, much of the rebel army was thrown into chaos after their leadership was destroyed, with daimons hunting down what remained as they fled into the forests. While human naval ships did little to actually assist Poseidon against the monsters, they had help him clear the lesser creatures that filled the skies over his oceans. Poseidon, utilizing every advantage he had, flew into battle against the beasts who dared invade his territory by sending deadly streams of pressurized water, electrical hurricanes that swept the skies, and vortexes that dragged his enemies into the deep abyss of his oceans.

Underworld
The armies of Gaia had managed to bypass Charon, the Rivers, and Cerberus with the assistance of traitorous daimons and attacked the heart of the Underworld itself. In the Realm of the Dead, however, the Shade inhabitants significantly outnumbered the invaders, reflecting the nature of Hades' realm. To ensure the Pit of Tartaros was keep from the invader's hands, Lord Hades himself took to the field of battle alongside his associated daimons and Cerberus.

Having lost their momentum nearly instantly by being drowned by shade warriors and led one of the Trinity, Gaia's invasion of the Underworld ended within only a few days.

Aftermath
In the days following the ending of the primary assaults, the Olympians proceeded to hunt down any and all dangerous elements within the realm, including perceived traitors and allowing the Erinyes free reign to track them down. Any and all residents of the realm who once was supportive or felt pity for Gaia's previous punishment quickly found their opinions changed about her as her rebellion brought destruction to many of their homes. As for Gaia herself, the Enduring Womb was taken from the fallen Primordial and she herself was finally imprisoned at the very bottom of Tartaros.

The monsters that survived the war largely fled back to Earth itself, only to be spread across the lands where their stories spread. Those monsters who could adapt to their new situation, rather than continuing their rampage, were allowed to live so they could provide a challenge to future heroes.