A Millennial Challenge: Extremism in Uncertain Times.

This comment highlights the relevance and importance of the uncertainty-extremism topic, both scientifically and societally, identifies common themes, locates this work in a wider scientific and social context, describes what we now know and what we still do not, acknowledges some limitations, foreshadowing future directions, and discusses some potential policy relevance. Common themes emerge around the importance of social justice as sound anti-extremism policy.