Second Ecumenical Council

The Second Ecumenical Council or First Council of Constantinople took place in 381. It differentiated the faith from Arianism, which was accepted by churches in the West. However, is declared Constantinople as the new center of the Christian faith, which was clearly not accepted by the Roman Catholic faith.

Reference

First Council of Constantinople

https://www.newworldencyclopedia.org/entry/First_Council_of_Constantinople#The_proceedings