Let's talk about how Joy Boy died 800 years ago and the world government formed during the void century .
We know Joy Boy was the strongest being of his time who was like a king to his people and was called Sun God Mika .
He was just like Luffy who doesn't care about anything until it means something to him .
So I think his death was not because someone just fought him and he lost to that person , but I think his death was due to betrayal within his own crew .
We've seen regret in apology many times in anything related to the ancient kingdom .
For example , the poneglyph of Fishman Island was an apology by Joy Wood perhaps because he knew he was going to die .
When someone in his own crew betrayed him , he died due to deep trust in them .
We've seen similar themes many times with Luffy too .
That's why Zumeshit is still walking with pain in its eyes after centuries .
And also after the giant robot's apology to Joy Boy , upon waking up , it makes even more sense .
I think the person who betrayed Joy Boy was Emu , who was part of his Dawn Pirates crew .
Also , Devil Fruits came into existence after the death of Joy Boy .