Although it was difficult for the Anu to survive on Earth without any help, they were scientists, and they were far more brilliant than the smartest humans, so it took them only a relatively short time to start rebuilding a level of technology.
Still horrified by what their race had done on Earth, they decided to build a communications array that would reach back to their home world. To place it high enough to escape the dampeners from the ship, they worked together with the humans to build a very high tower. The humans called this tower the “gateway to god”, in their language: "bab-el".
They attempted to create this tower of bab-el and nearly succeeded, until the military found them and again scattered and confused them.