what did Christianity have that the pagan religions didn't/ how does what was originally an obscure sect of Judaism become the official religion of the Roman empire..
Here's my previous answer to a quite similar question. Tell me if there's anything it doesn't cover, feel free to ask follow up questions.
Does anyone have an explanation specific to the Northern countries? Paganism seemed a pretty democratic religion (although crazy violent), so I'm curious to know why christianity was massively embraced by the population..
In Denmark at least, Christianity is believed to have been embraced because of the political benefits at the time. Harald Bluetooth is said to have made Denmark christian in 965.
The German Emperor threatened to invade Denmark and "kill the filthy heathens" because his God said that it was good. So to protect his country from the pressure of others (and to gain some powerful allies) he "made Denmark a Christian country".
At least, according to himself. This was political spin, seeing as there were small christian communities. They were a minority, but lived peacefully side by side with Vikings and Norse people.
In reality, only the nobility was christian (other than the small communities). There's proof that the common people still worshipped the Old Gods up until thte 13th century even (though fewer and fewer as time goes by).
Fun historical note: Harald's son Svend Tveskæg (Sweyn Forkbeard) led a rebellion against him through a bloody war and won the country in a battle against Harald.
An old story has it, that Harald commanded a great stone to be moved from one side of the country to another. As a man saw this, the King asked him, if he'd ever seen a greater burden pulled by men. The man answered: "I have seen Svend pull all of Denmark from your hands. You judge which burden is greater".