The heroes never would have been able to defeat the Nazis if not for the help of a hero of Earth-X known as the Ray.
Luckily, we have Freedom Fighters: The Ray to answer some leftover questions.
Evil versions of Green Arrow and Supergirl led the invasion along with Reverse Flash, and they wreaked a lot of havoc before the heroes were able to defeat them.
The crossover didn’t reveal the Ray’s origin story or explain everything that happened on Earth-X to led to the invasion.