Pagans / polytheists would respect other people’s gods. They would even worship them at times. They saw gods everywhere and in everything. One reason the Jews were seen as so weird was that they had one god, and refused to worship any others, but their culture was recognized as very old so the Romans respected their god as very powerful.
The Christians had the baptism ceremony, and part of being baptized is to forsake all other gods from this point forwards. Barbarians / pagans knew the Christian world as quite rich - the Vikings called Constantinople “the big city” and knew it as the place where they could sell all the cool stuff they stole during raids. A missionary would go to the barbarian leaders and tell them about their powerful Christian god, which was why the Roman empire(s) they fought were so grand and powerful. It was like a mind virus where one chieftain or leader would convert, win some battles, then assume the reason they won was their baptism. Because Christianity required ending worship of all other gods, they would aggressively convert the people under their control, and their nobles under them.
This is profoundly simplistic and overgeneralized. Religious tolerance was rarely strong anywhere in the pre-reformation (really pre-Liberal) periods. The Greeks and Romans have a long history of purging undesirable populations based on religion or ethnicity. Some pagan groups were famous for their tendency to massacre other pagan groups based on different god-worship, and Japan, China/Thailand's histories share this trait. To say nothing about the Assyrians, Babylonians, Scythians, etc.
The second part is also simplistic - The conversion of Rome into a "Catholic" country has more twists and turns and varied greatly across Europe and Asia. There was no true single church. The reasons for individual conversions were varied - some truly believed, some saw the tactical or strategic advantage, and some reflected their own population's beliefs. Some where given power if they converted. Much of the early conversion to Christianity was driven by women, not men and was household based. Even at a macro level it's instructive to look at the Germanic tribes, the Huns, and the British. All of whom had very different paths to eventual membership in Christendom.
Dan Carlin has a easily approachable set of podcasts about this, that I highly recommend.
It is very hard to give details in a brief comment. It is certain that many converted out of genuine belief in the Christian god. That does not change the fact that converting from one religion to another was not without reasoning. There is myriad reasons but the general take on my comment is accurate. And it was quite common when visiting other cities to pay respect to the god(s) of that city in the pagan world. This is why many victories would involve desecrating or stealing the religious idols contained in the defeated city’s temples. Even if that city’s god was not your god, seizing the physical nature of the god was seen as a good thing as it enhanced your power and hurt your enemy.
They stole the other parties' gods to prove that their gods were superior or true and the other gods were inferior or nonexistent. For example, see
Sennacherib's destruction of Babylon's temples and the replacement of Marduk with Ashur as the spiritual backbone of the neo-asyrian dynasty. Liekwise the babylonian destruction of the first temple, or the Roman destruction fo the second temple.
The trade routes in ancient times were advanced, as well as communication channels. As Egypt traded with other kingdoms and also intermarried, they respected each others’ gods. I reiterate that the Christian attitude towards other gods was different than the pagan attitude, where even within the same religion many gods existed.
I’m a practicing Catholic but I am a passionate consumer of history in many different forms. I agree there is genuine belief but it’s unlikely to me that a Jarl in Norway woke up one morning and thought “today I shall be baptized!” and suddenly renounced all of their ancestors and prior beliefs. There is a path from A to Z and I believe it always included tangible benefits in their reality. Things they can feel and see. This is why I believe in Christ so deeply - I know it to be true with what I have felt and experienced.
There really isn't a need for missionaries today. The Catholic church recognizes the concept of the virtuous pagan, which is really their attempt to handwave away some really deeply troubling implications. But they chose their poison, and they have drank it, and now catholics must deal with the consequences.
The concept of the virtuous pagan is thus: what if someone never hears the word of God, but is otherwise moral in their conduct? They will be judged as a Christian, whereas someone who rejects the word of God is destined for damnation.
Hypothetical: Gerald is a virtuous pagan. A missionary tells him the word of God. He rejects the word of God but continues to live his moral life. He is now going to hell because of that missionary.
I maintain that missionaries do not save the damned, they damn the moral. Please stop trying to recruit for your cult, just be happy meeting in your congregations, stop spreading the fucking gospels to people who are just sick of hearing that shit already. Goddamn. It's not special or important, it's just spiritual opium for unhappy people, to give them something to look forward to in death while they turn their noses up at people in life and act superior.
What a disgusting and astonishingly ignorant response. You're distorting things and your vulgarity betrays your hateful bias.
First of all, it is essential to Christianity to spread the truth of the Gospels. It is not optional. Christians have been commanded to do so by someone they take to be the Lord of the Universe. If you accept that, then it is necessary. It becomes an act of selfless love, to bring light to the darkness so that people may be saved from the darkness of sin. It isn't just missionaries, but every Christian has this duty. That's nonnegotiable. Your dislike of evangelism cannot change that.
Now, how it is done is a matter of judgement. Usually, it's a matter of demonstration, of living one's life according to the moral and divine law, and through outward signs that make known one's beliefs to other people. When someone lives a good life, this example inspires other people to learn more about the person in question, to better understand where this goodness comes from. Thus, the message of the Gospels can come out in a natural way during normal conversation, and when inspired by example, tends to carry more weight with people. If you genuinely accept the propositions of Christianity as true, then your speech and actions will reflect that. You don't need to strain and look for artificial ways to breach the subject.
Second, you speak of the Church like it has been composed of a succession of idiots who just recently realized the "implications" you propose. Yes, we had to wait two millennia before some guy on the internet or some pamphleteer finally realized there's an elephant in the room (never mind that Christianity started small in a backwater of the Roman Empire). Talk about cringe.
The Church still holds, as it always has, that baptism is necessary for salvation. Now, just because the sacraments are supposed to furnish us with certain graces doesn't mean God Himself is bound by the sacraments. Imagine our pagan forefathers who lived and died a thousand years before the Incarnation. They could not have possibly come to know Christ in the way the Gospels make evident. However, they could still have recognized and lived according to the moral law. Christ is the Incarnate Logos, so if you accept the moral law, you have, to some degree at least, accepted the Logos. Thus, if you come to know Christ through the Gospels, and you recognize in Christ the Incarnation of Reason Itself (that's what John 1 is about[0], though anything but the Greek do it justice), of this moral order, then why would you reject Christ? It makes no sense. The only answer is either a failure of recognition, or that one consciously rejects the Logos, of reason and morality, as evil people do (and all sin is a minor or major rejection of Logos). And if some form of invincible ignorance is indeed responsible, then there is no fault. Here's a bit more on the subject [0].
Cringe is trying to push your beliefs on other people because sky daddy commands you to. I'm not reading anything more on Christianity or catholicism, not after my early youth was squandered by moralizing hypocrites. Religious trauma is a very real phenomenon, and I'd argue that it's on the rise. Christians need to take a serious look inward and try to figure out why it is their religion of peace leaves such a wake of devastated souls and relationships. I actually saw two Christian parents, wholly bought into the fertility cult aspect, encourage their daughter to not seek cancer treatment because it might render her infertile. This is not an isolated attitude.
Also, why should it matter to me if they're doing it because they think they're commanded to by some omnipotent figure? I regularly disregard the rantings of schizophrenics, why should I buy into one delusion and not another? Why should I respect Christian beliefs more than other delusions?
I don't know why anyone is reluctant to believe in your assessment. While not Catholic now, I recall all the saint-worship in catholic school, which, as you probably noticed too, consisted almost solely of those that converted their own tribe of pagan barbarians for the period between Rome's fall and the Spanish Inquisition. Saint Boniface, Saint Patrick, etc. They pretty much declared people anointed demigods to be worshipped forever as reward for convincing barbarians that all their problems can be solved by the cross.
The Christians had the baptism ceremony, and part of being baptized is to forsake all other gods from this point forwards. Barbarians / pagans knew the Christian world as quite rich - the Vikings called Constantinople “the big city” and knew it as the place where they could sell all the cool stuff they stole during raids. A missionary would go to the barbarian leaders and tell them about their powerful Christian god, which was why the Roman empire(s) they fought were so grand and powerful. It was like a mind virus where one chieftain or leader would convert, win some battles, then assume the reason they won was their baptism. Because Christianity required ending worship of all other gods, they would aggressively convert the people under their control, and their nobles under them.