Jack Matthews wrote
Blood and the meat of strangled animals fall into the same category, but the reasoning is not as obvious to us today as it was in the time period when this took place. There was a blood cult in existence at the time, related to a piece of writing called the (sp) Tarobolium. In making accusations against Christians, their belief in the blood sacrifice of Christ was often linked to the practices of this cult, which mainly used cattle or oxen, in their rituals. They would strangle the animals, then cut their throats and turn them upside down, while a priest would stand underneath and literally "shower" in the blood.
Where was this blood cult located? Since Gentile Christianity was relatively new at this time, I doubt they were just reacting to a pagan cult. It makes much more sense that they were commenting on the teaching of Scripture. If you study the developments in Judaism in how Jews viewed the Gentiles, that sheds a lot of light on the subject. The Jews' 'rabbis', since before Christ, and after, debated whether or not to be righteous, a Gentile had to become a Jew through prosetylization (incl. circumcision) or if he could stay a regular uncircumcised Gentile and be righteous.
Non Christian Judaism came up with 7 Noachide principle sthat Gentiles had to follow to be rightoues. One of them involved not eating a piece cut from a live animal. Others were no idolatry, sexual immorality, the need for courts of law, etc. Basically, in theory, these things were supposedly extracted from the covenant with Noah, though they rely on other passages of the Old Testament as well.
It makes sense to view this passage as interpreting Old Testament teachings on Gentiles. James interprets 'DM to refer to 'Adam' instead of Edom when he quotes Amos. Since there were no vowel points, that makes sense. He interpreted the passage to show that in the end times, there would be 'man', i.e. nations of man, on whom the Lord's name was called, not just Hebrews.
From Old Testament times
Gentiles were not allowed to eat blood. God made a covenant with the ancestor of Jews and Gentiles alike,
Noah which gave mankind all kinds of meat to eat, but not the blood.
Leviticus shows that God drove Gentiles out of the land for immorality. So not only Israelites had to abstain from sexual immorality.
So James argued from what was revealed in scripture. Then he, and the elders, the 12 apostles, Paul, and Barnabas, wrote what is probably one of the earliest pieces of New Testament scripture we have, this letter from the apostles and elders. This is an apostolic command to abstain from things strangled and from blood. We can't just discount it because some cult somewhere drank blood.