degeneracy

dark age, nadir, sunset

decay, rotting, spoiling

breakup, crumbling, decomposition, disintegration, dissolution

abasement, debasement

depreciation, lessening

decimation, demolishment, demolition, desolation, destruction, havoc, ruin, ruination

abatement, decrease, decrement, de-escalation, deflation, diminishment, diminution, dip, downslide, downtrend, downturn, drop, drop-off, falloff, loss, lowering, reduction, sag, shrinkage, slip, slump

evil, immorality, sinfulness, villainy, wickedness

filth, gangrene, rot, squalor