what is a blood-feud tradition?
why/how was it banned?
If someone in your family kills another person, his family must kill someone from your family. Then your family has to kill one of them again, until one of the families is extinguished.
It was banned when Christianity came and the Kings became more powerful. Until 1200-1300 or so, Sweden was like a union of small kingdoms or tribal provinces. There were Kings over all of Sweden already before year 1000, but they didn't have that much power from the beginning. They couldn't even charge people with murder to start with.