[jxmvcoms] Erasure of discrimination without a social movement

Under what conditions has discrimination disappeared from society without a social movement?  Discrimination against the Irish, the Italians, the Romani seem to have largely disappeared in most of American society.  Similarly, there is not much Protestant-Catholic animosity.  In some parts of the country, there is little discrimination against Jews, Native Americans, or Hispanics, though in other parts discrimination persists.

The lack of discrimination is correlated with assimilation of these groups into mainstream society.  Which way is the causality?  (Previously, assuming one direction of causality.)  Or, there could be a common cause, or observation bias.

Certain subcultures lack certain kinds of discrimination seen in larger society, though that could be a result of selection (i.e., the observation bias above).

When (if ever) are social movements effective toward reducing discrimination?  Many of them invoke identity politics, which could worsen discrimination, the "racial nightmare" alluded to by Martin Luther King, Jr.