CA, I have read about the Christianization of Iceland in Icelandic. A really great story. I don't count it as an invasion because they voluntarily converted, which is why the books were not burned, which is why we have the Norse mythology in any decent extant form today.
For those unfamiliar, here's the story:
Harald Fair-Hair of Norway took over the country. The rich people decided they didn't like it, so they left to Iceland (Harald Fair-Hair is another favorite story of mine, but for an other time). So understand the culture of Iceland is a rich, literate people.
The Christians sent missionaries and, while converting some people, had little success. Those Icelanders just loved their paganism! Well, one summer, Gizurr the missionary is hanging out at the All-Thing with all the Icelanders and he heckles the law-giver: "I don't mean to blaspheme the gods, but Freyja is a bitch!"
Well, this doesn't set well, so Gizurr is given a three year outlawery (anyone can kill him, no questions asked). Gizurr leaves and comes back the next year to the All-Thing and gathered all his supporters together because the Icelanders were going to prevent him by force from entering the plain where the All-thing was held. So you have the fully armed Christians and sympathizers on one side, the fully armed Pagans on the other. And the law-giver that year, Thorgeirr, says "Now, now, hold on a minute. Let me go think this over." So Thorgeirr goes and takes a nap.
And they waited.
And they waited.
And they waited.
And the next morning, Thorgeirr comes out of his tent, and he says "Okay, I feel much better. Now, obviously the Christians are here to stay, so we kind of have to work something out. Their forces could overwhelm us if this breaks out into a war, so let's convert peacefully. Here's the deal, three things: you can't have a rune, you can't make sacrifices, and you can't have a horse phallus." (Because apparently the fun thing to do on a Friday night in Iceland was to pass a horse phallus around.)
And that's how Iceland became Christians peacefully!