It was neither. Most people have huge misconceptions about the Councils. They like to see it as the big ole bully church telling people what to believe. A look at the data will soon show that is rather a flawed assumption. Councils try to establish the truth in the face of contention, to head off the drift into error. Nicea, for example, was called to settle a Christological dispute, which, I might add, did not go away. The Trinity wasn't discussed, because it wasn't disputed. It was there from the beginning, spoken of by the Fathers in the 2nd century, and is still widely agreed upon today – Catholicism, all the Orthodox Patriarchies, Anglican, Evangelical, Lutheran, Presbyterian, Southern Baptist, United Methodists ... are all agreed on the Trinity as One God in three Persons ... I think I'm right in saying it's some American ideological denominations that don't accept the Trinity.