A group of Episcopal laity and clergy gathered in St. Louis, Mo., in 1977 and issued a statement of faith, known as the Affirmation of St. Louis. Its guiding principals are found in the King James Bible, 1928 Book of Common Prayer and teachings of the early church fathers.
The Affirmation of St. Louis is what generated the OPACC.
I have to say that I am not certain that all the signatories to the Affirmation of St. Louis are in communion. I don't know the particulars, but I have heard that not all the parties played by the rules established there.