I think that Sedna represents the demon figure that society creates in order to enforce it's own values and ideas, that which society rejects in other words. The Eris/Sedna conjunction in Aries (in the charts of those over about 30) unleashed Fascism onto the world, because it causes society (Eris) to become (Sedna), to Aries the demon-figure is the Tyrant, however the Aries Sedna demon-figures is the Anarchist.
For society to be it's own demon-figure, is a traumatic event, since Eris represents not only society as static, but also societies currents for change, then Sedna causes rejection both of society and of the currents of social change. Very Fascistic.
WW2 happens when Eris conjunct Hitlers Sedna within 2 degrees. In 1945, it perfectly conjuncts his Sedna, as Hitler is 'spat out' and becomes quite literally societies demon-figure.
Sedna and Eris were actually both in Aries, but not conjunct thankfully. This is I think a rare event, it certainly won't happen next time Eris moves into a new sign, which is a relief.