Need info on Squaller

[Veho Nex]

Ok so im playing today and doing really good i just finished conquering rome and all that and the rome west is decimated(playing as celts) and after i finished all that i started moving in on east rome but two turns in about half of my cities start revolting and when i check their happiness squaller is the only thing affecting it and no matter what i did they continued to revolt until finally 90% of my eastern empire rebelled and then i utterly lost that game so now i need info on how to stop squaller or at least make it less of a problem.