It wasn't just that Constantine made christianity the "official" religion of the Roman empire (he did), but he also sought uniformity of the faith. There were hundreds, if not thousands, of little isolated communities where some version of the abrahamic faith existed - many which had their specific "brand" or version of the faith edified by a writing. Hundreds of local religious leaders were invited, along with their respective books, to the first council at Nicea. It was then and there that the christian orthodoxy was established under arch bishop Athanasius ... who directed that Jesus would be viewed as a god, not a man, and any books that detracted from his divinity (or that of Mary) were immediately banished and their holy men were bound to accept the new direction at threat of death. This left out or significantly changed many belief sets and texts including the very popular Book of Enoch which was later included in the Ethiopian Bible and the Koran. But that's where the origin began for Europe and the orthodox christian beliefs.

I’m not the first to say it but I’ll reiterate it... it’s all about power. Every Roman Emperor wanted to rule the world. Most could care less about Christianity, they just knew that getting crowned “Holy Roman Emperor” by the sitting Pope was the key to power. Some Emperors even had Popes assassinated so their cronies could become Pope. Charlemagne is a prime example. His mission, because he wanted all the power, was to convert the holdout pagan Germanic Tribes to Christianity because it would bring him favor from the Pope. His plan for conversion was simple, convert or die. He rounded up thousands of pagan men and had them slaughtered in front of entire villages, including children. Christianity wasn’t built on love, it was built on fear. Always has been and always will be. It’s the first thing I remember learning from my catholic upbringing. If you don’t fear God and Jesus you will burn in Hell for eternity.

I think often people didn't have a choice but were force into accepting.

Bart Ehrman has written an entire book about called The Triumph of Christianity. His thesis boils down to this:

1)Christianity, unlike most Pagan religions, is evangelistic. Christians actively recruit non-Christians. and

2. Christianity, unlike Paganism, is exclusive. Christians insist that Christians worship their 3-in-1 God, and no other.

The combination of exclusivity and evangelism is powerful. Christians seek converts. If they manage to convert someone, that new convert will attempt to convert all their friends, every member of their family, and strangers as well to worship the Christian go--to the exclusion of any Pagan gods. You can see how this formula, exclusivity + evangelism, could lead to exponential growth.

Most Pagan religions are neither exclusive nor evangelistic. They don't care to convert others to their gods--and if others do convert, they don't have to give up their former gods. They eventually were swamped by the growth of Christianity. This makes sense to me. What do you think?

“Follow the money.”

The Catholic church did a good job of co opting local religious beliefs in order to somewhat appease those they were converting by coercion. Give up your gods and convert--or die--is a strong incentive to convert.

Their choices were convert or die. And after enough nonconformists were slaughtered, resistance became all but untenable.

Roman emperor Constantine took on the religion to win a battle, made it a state religion and commissioned churches all over Europe to spread the religion. Because it puts slaves in their place it worked very well for the slave society of the time.

Christianity was one of many fringe religions when Rome rules the world.
In 306 Constantine was declared emperor by his troops (in York, England and began a military campaign to take power.
n 312, Constantine fought at the Milvian Bridge on the Tiber River. Accounts state that, following a vision, Constantine ordered a Christian symbol to be painted on his soldiers' shields, was successful in battle and entered Rome.
Constantine, as Western Roman emperor, issued the Edict of Milan in 313, legalizing christianity and allowed for freedom of worship throughout the empire. The Council of Nicaea in 325. Out of this came the Nicene Creed, which affirmed that Jesus was a divine being.
Constantine was baptised, shortly before his death on May 22, 337,
Thus christianity became established as a going concern.

Constantine. And Paul. It was politically expedient for Constantine, especially since Paul had made it Roman.

It was co-opted by Rome.
To be used to control the masses.

If you were a warrior and were killed in battle you’d get to be with Woden in Valhalla, assuming I suppose that you were a follower of Woden. But in general only gods and goddesses were immortal. So Christianity must have had appeal since it offered everlasting life.
By coaxing yourself into belief, supposedly a person can worm his or her way into heaven. That’s because of the crucifixion BTW. Makes total sense, aye?

Also the teachings of Jesus have a certain appeal in a social way. I can see how the leaders might use Christianity as a means of taming our wild and savage ancestors of Northern Europe who were constantly fighting and killing.

I don’t see much sense in those pagan gods and goddesses. You had to offer them sacrifices or they were liable to give you some real crap. Maybe adopting Christianity was a step in the right direction, and now it’s time to move on to more advanced religions that are in accord with science.

Fear. When Constantine became emperor (3rd Century) and decided to adopt and promote christianity, it became the official religion of Rome, ergo the western world. That is the simplified reason.

Emperor Constantine made it the religion of his empire.

You might be interested in a book called The Darkening Age by Catherine Nixey. It is an interesting account of the coercive processes by which Christianity supplanted earlier beliefs and became the official religion of the Empire. According to her (and I've no reason to doubt her) there was nothing spontaneous about it and no free competition between competing religions.

Control and sex. Most pagan religions are sensual. Christianity is more attractive to dickless priests.

Simple human stupidity.

accept?

genocide?

Blame it on Pope Leo III, who crowned a Frankish War Chief (Charlemagne), 'Emperor of the West', with the assigned task of forcing European pagans to accept Christianity.

Blame Rome.

There was convenience on the simplicity of moving from many gods to one god. We have now found convenience on the simplicity of moving from one god to zero.

A roman emperor needed mercenaries and the early Christians offer their help under condition of his conversion. ‍

Just as cultures evolve, so do religions. Yahweh is an adaptation of many of the local religions at the time

don't know why the european tribes accepted christianity. i can understand why eastern europeans & others accepted judaism. the jews were usually successful where ever they settled. why not follow a religion in which the ppl seem to be successful & well off?

Rome was the big cheese culture. So even if you were not occupied like Ireland. It must have been very influential. Just as Hollywood and rock-n-roll have been exported from the USA.