As much as I can gather, the One Being was a threat to the Elder Gods, so they smashed it with the Kamidogu creating the Realms. Since they knew that the Kamidogu could be used to reunite the One Being (bringing an end to all existence), they split the weapon into 6 pieces and hid them deep across the Realms.
Then comes MKD, where Shujinko is decieved into reuniting the Kamidogu, causing the whole mess seen in MKD. Raiden is angry at the whole of humanity for (what he considers) Shujinko's foolishness.
The thing is, since it's possible for a mortal to utterly destroy the pieces of the Kamidogu (ie. in the battle with Onaga), then why couldn't the Gods? Since they decided to hide them instead it was an 'accident' waiting to happen! Raiden should instead be blaming himself and his fellow Gods!
If they can split it in 6 pieces, and humans can destroy it, then why DIDNT the Gods destroy the Kamidogu in the first place?

Please include a spoilers warning when revealing the entire plot/ending of Konquest mode. ~Crow~