It is explained in the story that it has been 1,000,000 years since the Dino Knights had last defeated the Dragozaurs. The Dragozaurs have returned, a boy named Kaito has reawakened them. The battle between the Dino Knights and the Dragozaurs begins once again as the Dino Knights prevent the Dragozaurs from stealing Earth's life force.

(Source: Wikipedia)