What is the story behind Dragon Ball Z

You can read this brief over view or you can wath dragon ball (the series before dragon ball z) and get a better picture.

well this is a very long story but basicaly there was a boy named goku who landed on earth. He was from a different planet called Vegeta his race is called the saiyans. They are forced to destroy and conqure planets. They send babies to week planets and adults to strong planets. When goku arives on earth. He is naturally aggresive because of his saiyan blood but he gets hit in the head and becomes a sweat boy. He is adopted by a martial artist and learns how to fight. The thing about saiyans is as long as they have a tail they turn into a monster at full moons and since he is only a boy he has no control. He accidentally kills his adopted father. All he left behind was a dragon ball. Goku lives alone for a while but later meets a girl named bulma and she tells him that if you gather all 7 dragon balls you get a wish. They have a long adventure wich im not going to go into right now but he makes alot of friends like yamcha, roshi, oolong, puar and the ox king aka his future father in law. After that he trains with krillenfor a while under master roshi. Then he goes off and trains with other people. He loves to test his streangth every three years at the world martial arts tournament .there he meets tien and choazu (by the way im not 100% sure im spelling all of this right) and later he meets piccolo who tries to take over the world but is stopped by goku. Goku lets him live but piccolo swears he will take over the world and destroy goku eventually. Dragon Ball z picks up a years later when goku has a son and wife.