  Based on a dynamical model with fractional derivatives we show that the
evolution of radical groups in a society with a memory depends mainly on the
active proselytism of radical groups and the level of cohesion in social
networks. We find the conditions that determine that the radical group either
disappears or, on the contrary, achieves a permanent significant expression. We
also discuss the possible intervention strategies on the susceptible population
and show the conditions that lead to the disappearance of radical groups. We
see that the higher the level of memory, the maximum proportion of radicals
decreases, but those groups manage to maintain their presence in society during
a larger period of time.
