After Adolf Hitler escaped into space to avoid destruction about 3000 years ago, he and his loyal followers landed on Jupiter. There, they lived on, passing power through the line of Hitler's descendants to the current leader, Ralph Hitler. As a child, Ralph was bullied and had his lunch money taken away, which combined with his natural hatred of humanity to mold him into pure evil. He seeks the annihilation of all life-forms, and his army of Space Nazis supports him.
Also the Space Nazis have lazer vision. Thanks to eye implants.
Needless to say, the Jupiter Space Nazis will not permanently ally with anyone, but they're quite happy to lend a helping hand when it comes time to reduce a planet to smoking rubble.