Highschool DxD season 2 episode 24


this anime has certainly been a confusing one but up until now ive been following the story quite well, im at the end of season 2 and naturally so much has occured in the final epsiode of this season, would somebody mind explaining to me what the chaos brigade is and what occured during the leaders summit, all this talk of gates and decendents of devil kings has fried what little of my brain i have left i have tried to find a summary of episode 24 online but unfortunately i cannot find anything, a general explanation of the events in this episode would be greatly appreciated since it has left me completely baffled. 😂😭