It wasn't just Last Lights preparing for Averoth's Vault.
Salamandor was also in his preparation phase. With his abundance of clones he began to spread the rumor regarding the vault in the most contagious way: gossip.
Making comments in taverns and restaurants. Exchanging the information in various circles. Even acting like the information was confirmed by "sources" that did not exist. He used every method all to gain the attention of all major players interested. That was of course the Kingdoms.
It was a very fragile time for conflict. Just about every Fourth Stage was on an expedition elsewhere. Even the mighty Gated Arena only had a handful of their usually abundant numbers. Meaning only a handful of truly powerful individuals could be deployed to the Vault.
None of the Kingdoms dared to risk these individuals for a squabble. If something were to happen then their entire Kingdoms would be helpless to any attacks from other Kingdoms.