that each kingdom has a maximum of treasuries.
It has already happened that a single kingdom has half the map for it, or that a single kingdom is too far from the others.
Limiting 10 treasuries per kingdom (union included).
the game would be more entertaining since there would be more kingdoms, and not only one kingdom took 4 wonders.
Currently in kingdoms you, you enter, look at the kingdoms, join and win the server. It doesn't make much sense for a single kingdom to take 4 wonders or have 70% of the players.
another suggestion for kingdoms, like all the others : D