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]