Norse mythology and several other Icelandic literary works identify that there are two tribes of gods and goddesses; the first tribe being the Aesir and the second one being the Vanir. The two tribes are quite different from each other. The Vanir were more elderly and entirely pacifistic, while the Aesir gods were more warlike and directly represented the strength found in natural elements. Despite their differences in character, the two tribes seamlessly coexisted with each other and lived in peace. However, there was a time when they had some kind of tension between them that entirely affected their relationship.
Freya, the Vanir goddess of beauty and fertility, was a master of Sedir, which was considered the worst yet most powerful form of magic in Norse culture. She regularly wandered across the 9 realms in search of clients for her Seidr services. She disguised herself as Heidr when she was getting closer to Asgard, and when the Aesir gods and goddesses learned about her magical prowess, they immediately sought her services.
As time went by, the Aesir started to realize that their selfish desires and quest for Seidr were starting to damage their values of honor, obedience, and kin loyalty. When this happened, they all blamed Heidr (Goddess Freya) for their individual shortcomings and greed. By the time all the gods in Asgard were affected by the Seidr, they named Freya Gullveig. The name Gullveig meant ‘gold digger/gold-greed’ and tried to get rid of her.
They tried to burn her 3 times, but every single time they did, goddess Freya was reborn from the ashes. This scared the Aesir and they concluded that the Vanir had even more magical powers than the Seidr. Their fears slowly turned into vigor and lots of tension. Eventually, the clash turned into a brutal battle between the two tribes of the gods. The Aesir used weapons and brute force during the war, while the Vanir settled for magic, particularly Seidr. Each of the gods wanted to emerge the victor in the war, but the war didn’t seem to stop.
Eventually, the gods were running out of resources and became weary from the way, so they decided to call a truce. Generally, the Norse believed that two opposing sides are to pay tribute to each other after every war. In respect to that rule, the two tribes decided to pay tribute to each other by exchanging. The Aesir gods sent Mimir and Hoenir to Vanaheim to live among the Vanir gods and goddesses, while Njord, Freya, and Freyr, were sent to Asgard to love among the Aesir gods.
The Vanir gods and goddesses who went to love in Asgard lived peacefully and were easily integrated into the Aesir family. However, Mimir AND Hoenir had a pretty difficult time in Vanaheim. Mimir could not function without Hoenir on his side and Hoenir was a slow-witted simpleton hence disregarded by the Vanir. Because of the shortcomings that the two hostage Aesir gods had, the Vanir gods were convinced that they were duped by the Aesir.
To get back at the Aesir, the Vanir beheaded Mimir and sent his head to Asgard. However, that didn’t move Odin. Instead, Odin embalmed Mimir’s head with herbs and enchanted poems over his head so that Mimir could always advice Odin when needed be. This made the Vanir angrier, but they could not fight because their resources and energy were completely depleted from the initial war. So, the two tribes decided to spit on a cauldron as a way of pledging harmony between them no matter any challenges that arose in the future. To avoid wasting their saliva, they created an intelligent and gifted being known as Kvasir, who helped the Aesir and Vanir when in need.