How did Oneness Pentecostalism spread and grow during the 20th century?

[Oneness Pentecostalism](https://en.wikipedia.org/wiki/Oneness_Pentecostalism) is a movement within the broader Pentecostal movement which rejects the Trinity [and is essentially a revival of Modalism](https://christianity.stackexchange.com/a/33133/6071) . Oneness Pentecostalism arose shortly after Pentecostalism itself. In the USA in 1916 the newly formed Assemblies of God fellowship officially affirmed the Trinity, and ["a third of the fellowship's ministers left to form Oneness fellowships"](https://en.wikipedia.org/wiki/Oneness_Pentecostalism#Beginnings_of_the_Oneness_movement) . Throughout the twentieth century Pentecostalism spread quickly throughout the world, so that [there are now](https://en.wikipedia.org/wiki/Pentecostalism#Statistics_and_denominations) close to 300 million Pentecostal Christians, 13% of all Christians, and 4% of the world population. Oneness Pentecostalism is much smaller, with only an estimated 24 million adherents, but there are still a lot of Oneness denominations: based on [stats from Barrett, Kurian, Johnson's *World Christian Encyclopedia*](http://www.philvaz.com/apologetics/a106.htm) there are at least 414 Oneness Pentecostal denominations.1 What is an overview of how Oneness Pentecostalism spread and grew during the twentieth century? What sort of mission strategies did the movement have? Did the American Oneness churches start foreign mission efforts immediately, or only after some time? Were there united mission agencies, or did each American denomination work independently from the others? Did they generally focus on evangelising to non-Christians, or did they also aim to convert Trinitarian Christians to the Oneness doctrine? --------- 1. Their methodology counts each counts each country's denominations separately, so that there are 242 Catholic "denominations" and 168 Anglican "denominations", so all such denomination numbers may seem much larger than expected.