Anti: The opposite of
Dis: The absence or opposite of.
(Double negative = excess wording)
Establishment: See here.
Arianism: Arianism is the theological teaching attributed to Arius, a Christian Presbyterian from Alexandria, Egypt, concerning the relationship of the entities of the Trinity ('God the Father', 'God the Son' and 'God the Holy Spirit') and the precise nature of the Son of God.
So. Establishment of Arianism, I take it.