Flash Gordon: The Greatest Adventure of All

Ming the Merciless has secretly supplied military technology to Hitler, using Earth's World War II as part of his divide-and-conquer strategy. This connection explains why Earth is under attack and why Ming wants to destroy humanity, he's manipulating both worlds simultaneously to achieve domination.

Earlier in Warsaw, the dying contact's warning about Mongo hints at Ming's involvement in Earth's conflict.

Flash and Dale Arden find Doctor Zarkov's hidden rocket ship in a cave after their plane is forced down by meteorites. Zarkov explains he built the ship to travel to Mongo and stop their attack on Earth. The trio launches together, but hostile Mongo ships shoot them down before they can make contact, forcing a crash landing on the planet.

Zarkov built a rocket to reach the wandering planet Mongo, which is attacking Earth with a gravity weapon. His plan is to persuade Mongo's rulers to call off the attack through diplomacy, but he's prepared to use his own gravity weapon as a last resort if negotiations fail.

The dying contact in Warsaw whispering 'Mongo' sets this mission in motion.

After escaping captivity, Flash meets King Thun of the Lion Men and learns Ming uses divide-and-conquer tactics to subdue his enemies. To fight Ming's robotic army, Flash unites Prince Barin of Arboria and King Vultan of the Hawkmen into a resistance coalition, pooling their forces against the common enemy.

Ming unleashes his Mole Men against Arboria by having them destroy the fibrous forest roots that provide camouflage for the kingdom. Zarkov warns Flash about the attack in time for them to seize a captured drilling machine and use it to strike Ming's palace, turning the enemy's weapon against them.

During the final duel, Flash discovers that the Ming he fights is actually an android impostor. The real Ming escapes while his robotic double battles Flash. This revelation shows Ming is a coward who uses deception and automation to avoid personal risk, and he remains at large as the battle concludes.

With seconds before Mongo collides with Earth, Flash follows Zarkov's plan and damages Mongo's drive system. This action nudges the planet off its collision course, diverting it away from Earth and preventing the catastrophe. The immediate threat is averted.

Although the android impostor was defeated and the real Ming fled, Flash and Dale successfully saved Earth from destruction and helped liberate Mongo from Ming's immediate control. They decide to stay on Mongo together, looking forward to a new life of wondrous adventure, making the ending happy despite the unfinished war.

Ming maintains power over Mongo by keeping his kingdoms isolated and attacking them separately rather than allowing them to unite against him. King Thun explains this tactic to Flash, noting it's the same strategy Ming employs on Earth by supporting Hitler, keeping enemies fractured makes them easier to conquer.