The opposite of pejoration (worsening) would be amelioration (building, strengthening).

Amelioration in terms of slavery is the policy of improving slave conditions.

An amelioration is an act of ameliorating - of making better or improving.

The word disambiguation refers to the process of trying to resolve conflicts that arise when a single term is ambiguous. Disambiguation seeks to have clarity from ambiguity.

In the year 1830, amelioration totally ended so that emancipation could have been achieved.