Probably a broader/deeper POD than you wanted @djPROUDGEEK, and pre 1900, but the LDS angle is most likely to get you the result. I'm thinking if we managed to rearrange the SW territories and subsequent states it'd the most interesting means of killing gambling. Keep Nevada part of the Utah territory. Keep NM territory or divide it. (Assuming NM legalizes gamblubg, keeping it whole permits you to have legal gambling right across to border from California.) Delay most of the mining finds in Nevada, and you can work it that way - I think.