Complex sentence: So, the idea of a common enemy is a symbol of the evil against which people must unite, and it distracts the people from politically inconvenient issues by relating all evils to the common rhetorical enemy.
Split into simpler sentences: So, the idea of a common enemy is a symbol of the evil against which people must unite. This rhetoric distracts the people from other significant issues by relating all evils to the common rhetorical enemy.