General synonyms:
* Decline
* Deterioration
* Degeneration
* Corruption
* Depravity
* Dissolution
* Luxury (in the sense of excessive indulgence)
* Self-indulgence
* Excess
* Moral decay
* Cultural decline
* Downfall
More formal synonyms:
* Effeminacy
* Dissolute
* Debauchery
* Vices
* Luxury (in the sense of extravagance and indulgence)
More specific synonyms, depending on the context:
* Sophistication (if referring to a decline in traditional values)
* Overindulgence (if emphasizing excessive pleasure)
* Decay (if referring to physical or moral deterioration)
The best synonym will depend on the specific context and the intended meaning.