How did batman become a part of the justice league?

In the very first episode aliens were attacking earth and superman and batman were trying to stop it alone. Then a good a Good alien Otherwise known as Martian Manhunter wanted to help. so he contacted Wonder Woman, Flash, Green Lantern, and Hawk Girl to help. They eventually defeated the aliens. After all this Superman wanted to make a justice league after he saw how everyone worked together and everyone agreed. That's how the Justice League came around with everyone in it.