"Virtue signalling" in European-rooted cultures stems from classical Protestant (especially Calvinist and Puritan) esteem for right belief over good works. Good works were seen as cheap and fake and worldly, while right beliefs indicated alignment with a more eternal truth.

While not the only current in American history by any means, it's profoundly American, and you can draw a straight line of intellectual heritage from that core Puritan/Calivinst theology on through to Rauschenbach's Social Gospel theology and onto the modern secular Social Justice movement, spanning hundreds of years of American history.

Historians of the future will have been trained in the postmodernist university system of today.

The core tenet of postmodernism is that there is no objective truth, everything we see in the world is a societal/human construct. It's a pants-on-head extremist outloook that allows absolute insanity to parade as intelligence. It's reasonable to assume that there is at least some semblance of objective truth and argue about the degrees.