The one single event that probably most influenced the early development of Christianity was the decision of Paul to permit gentiles to become Christians without the trauma of circumcision.

Yes, it was a controversy between the Donatist sect in Tunisia and the Bishop of Rome in the early 4th century B.C. The Roman emperor Constantine the Great unsuccessfully tried to mediate it.

The tariff controversy of the early 1830's showed that the nation faced serious and growing sectional pressures in the years ahead. (:

There is no specific year, but circumcision of converts to Christianity was very rare to begin with. As is evident in the epistles of Paul and Peter, the practice was debated from the first first days of the church. By the end of the first century the Epistles of Paul were widely read, and by this time circumcision of converts had likely ended completely.

Society for the Study of Early Christianity was created in 1987.