Odin went with a great army against the Vanir. Each laid waste to the other’s land. When they tired of the war, they made peace and exchanged hostages. (This is from Snorri’s Ynglinga Saga, 4.) I use elements of this version in my books, but avoid the euhemerism in Snorri’s account (because it’s lame).
The seeress of the Voluspa recounts a different version of the war in which it began with a Vanir witch named Gollveig (possibly Freyja) who sought to bewitch the minds of the Aesir. The Aesir killed Gollveig with spears and then burned her three times, only for her to rise again.*
The seeress continues, saying:
On the host his spear | did Othin hurl,**
Then in the world | did war first come;
The wall that girdled | the gods was broken,***
And the field by the warlike | Wanes was trodden.
In both versions (Snorri knew the Voluspa, btw), the Aesir and Vanir made peace and exchanged hostages. Njordr and Freyr were sent to the Aesir; Hoenir and Mimir were sent to the Vanir.****
Njordr, Freyr and Freyja are the only known Vanir gods. Simek says that there was a Vanir named Ing who later become synonymous with Freyr. (I don’t include Ing in my books b/c I’d have to call him Ing the Erciless, and that’s not particularly funny.) I also don’t include Ullr as one of the Vanir.
Skadi, a Jotunn, married Njordr. Some accounts list Freyr and Freyja as the children of Skadi and Njord. Other accounts say that Freyr and Freyja are the children of Njordr and his (unnamed) sister. (Take that, GRRM! :))
My books assume that Njordr is married to Skadi*****, that Freyr is married to Gerd and that Freyja is married to Odr (who has been missing for a long time). All three of these marriages are extremely important for various reasons — both in myth and in my books.
In myth, the Vanir are gods of fertility though they also served other functions. For example, Freyja is also a magic, war death goddess (not unlike Odin). But, more on the individual Vanir gods in future posts.
My Vanir are as ancient as the Aesir, but originate in a different part of the world. They encounter the Aesir after they (the Aesir) fled their homeland and happened across fertile lands claimed by the Vanir.
Hostilities broke out. Each side inflicted great harm upon the other. After a time, they gave up on the war, made peace and exchanged hostages. Despite a rocky start, the Aesir and Vanir became close knit allies who helped each other against mutual threats (the Jotunn and the Svartalvar).
Essentially, my Svartalvar are to the Vanir (and Alvar) what the Jotunn are to the Aesir. All five groups (counting the Svartalvar as the 5th) are inextricably linked in each other’s messes — and that has massive repercussions for what happens in future books. While both Freyr and Freyja appear in my first book, they don’t assume central roles until those future books.
*Ouch. And, Simek suggests that this is too simplistic an interpretation; that may well be the case, but I’m not addressing it in this post.
**Hurling a spear over/into an opposing army was how the battle was dedicated to Odin (he’s the god of battle and many other things).
***I allude to this as the “old wall” in several scenes.
****Mimir was soon beheaded & sent back to the Aesir; Odin preserved the head with his magic and consulted it for advice.
*****At this stage, my backstory assumes that Freyr and Freyja are the children of Njord and his sister-wife.