For if someone comes and proclaims another Jesus than the one we proclaimed, or if you receive a different spirit from the one you received, or a different gospel from the one you accepted, you put up with it readily enough. I think that I am not in the least inferior to these super-apostles.

• 2 Cor 11:4-5

Corinth then later on full on deposed Rome's appointees which led to the letter from the bishop of Rome, 1 Clement that's almost entirely devoted to trying to damage control the schism.

And why not say (as some people slander us by saying that we say), “Let us do evil so that good may come”? Their judgment is deserved!

• Romans 3:8

I am astonished that you are so quickly deserting the one who called you in the grace of Christ and are turning to a different gospel— not that there is another gospel, but there are some who are confusing you and want to pervert the gospel of Christ. But even if we or an angel from heaven should proclaim to you a gospel contrary to what we proclaimed to you, let that one be accursed! As we have said before, so now I repeat, if anyone proclaims to you a gospel contrary to what you received, let that one be accursed!

• Galatians 1:6-9

You can even see some of the specific concepts that there was a schism about, such as whether there was an over-realized eschatology:

As to the coming of our Lord Jesus Christ and our being gathered together to him, we beg you, brothers and sisters, not to be quickly shaken in mind or alarmed, either by spirit or by word or by letter, as though from us, to the effect that the day of the Lord is already here.

• 2 Thessalonians 2:1-2 (likely a bit later than Paul)

Avoid profane chatter, for it will lead people into more and more impiety, and their talk will spread like gangrene. Among them are Hymenaeus and Philetus, who have swerved from the truth, saying resurrection has already occurred. They are upsetting the faith of some.

• 2 Timothy 2:16-18

So I'm not sure where you get the notion there was one big happy family of Christian thought in Paul's time and the later 1st century CE when literally the earliest records of Christianity we have are so concerned with competing traditions and ideas. You may be mistaking the survivorship bias of cannonical Christianity eradicating most competing thought later on for a picture of unity (as that's what they try to project) which is why a closer read is warranted.

Plus you know we have no evidence that Buddhism had that fighting after Siddharth death

It had that fighting even before Siddhartha's death when his brother in law Devadatta broke away to form his own group.

Mormons didn't break out into civil war after Smith died.

You might want to read up on the succession crisis

Scientologists are also doing fine.

You might want to look into the Free Zone schisms from Scientology near and after L Ron's death.