Basically, AJPW had two aces, Genichiro Tenryu and Jumbo Tsuruta. Tenryu left and created SWS, anyone know of this, lol, and so by doing so Baba basically was like "Tenryu will never wrestle in All Japan as I live", and so Jumbo became the ace. By this time, Jumbo was oldest member and he wanted to stay on top because as the meme goes "Fuck them kids! this is my spot and I will be damned if them kids take it from me." and so Misawa was like "Alright bet old man" so they began their rivalary and it was damn good since it was the old v new and you had the Tsuruta-gun v The New Generation Army, which was also great. So at the height of their carrer for both men, Baba decided to let Misawa win because he was so over and Jumbo began dealing with helath issuses so Misawa won and ethroned the old ace to become the new.
(This is just a short version of everything)