
Actually I misspoke. The council of Nicaea basically decided that Jesus was divine in essence, whereas the second council of Constantinople actually decided that the Holy Spirit was also God, meaning that for a whole 300+ years after Jesus started preaching, people didn’t actually think he was God and that the Holy Spirit was God either
Please do keep in mind I’m no biblical scholar I just have a weird interest in this. Arius - a priest - was teaching that Jesus was not in fact divine but was a created being (not 100% sure on that one, I’m not Christian) and his status was lower than God, which was contrary to what his archbishop was teaching (Jesus = God) and he accused his archbishop of following the teachings of somebody else, which was a contrary opinion to the majority opinion (God, Jesus, and Holy Spirit are separate)
People got mad and confused, and it went up the ladder until Roman emperor Constantine I called the council of Nicaea together to decide things. They ended up deciding that Jesus was divine to the same level of God, but made no actual mention of the holy spirits divinity, thus was the beginning of but not the first appearance of, trinitarian doctrine
There is SOME mention of the “trinity” extending to the early 2nd century, but it didn’t follow the “father son holy spirit” formula. It was authored by and was “God, his Word (Logos), and his Wisdom (Sophia)” so to say the Trinity didn’t exist is somewhat false, but it is entirely accurate to say the Trinity as followed in biblical doctrine in current times was not added to Christianity until at the very earliest the Second Council of Constantinople when the Holy Spirit was made divine and God