this series starts from Hot wheels highways 35 to really understand it you should watch these first. the reason the two gangs Teku and Metal Maniacs fight so much is the leader of the Metal Maniacs is accused to killing Teku leader Nolo Pasaro's brother Tone Pasaro. As the series progress though the four movies more about the teams are relayed and the point of the racing realms. i highly recommend watching 3 or all of them so you have seen the whole series. it goes Hotwheels Highway 35 AcceleRacers Ignition Speed of Silence Breaking Point The Ultimate Race