The Fall of Shrima an Accident

So I'm new to the lore of League of Legends. I guess I played the game for long enough to finally want to dive into the lore. Since I'm a filthy "Plus 12" player, I wanted to read on Nasus. From there I read Xerath's story. Reading through the rest of the Shriman Characters, Xerath's story gave me a thought. Xerath hated his friend Azir and to lure him to undergo judgment by the Sun Disk and die. But when Azir had finally followed on his word and as a possible last word if the Sun Disk killed him, friend Xerath, his life long friend from slavery and had banned slavery respecting Xeraths words. But Xerath had already planned Azir's death and wanting to stay alive didn't tell Azir he was walking into his death. So was the fall of Shrima all just an accident or is there more that I'm missing. Can someone please give me the full history of Shrima. I'm so interested and I want to really get into the lore of league.

Thank you all ImP Shot