All hail King Björn!
It has been a long time making but finally Björn isn't without a kingdom. Although I don't think he ever believed that he would reach the point, where the people would call him as a King. It's even stranger custom that one would be crowned after a battle, but I guess that's how it happened.
We are just so custom these days that the Royalties don't change after clashes. We are even more custom that those crownheads don't participate in the breakthrough battles, because of their sensitive status. Yet, back in the day, you'd hardly have a conflict without some noble taking part into swinging swords, or barking orders at the barriers.
I guess war changes. It certainly isn't like that at modern times. Vikings are lucky that they didn't invent gun powder or ventured far enough into the east to steal it from the Chinese, because that sort of war would have terrible. No walls could have stopped their advance, and our world would look certainly different.
Maybe it is a luck that we have such a low birthrates, because if the North had been full of people, the world would have changed more quickly. Can you imagine what North America would look like after the Viking invasion?
I certainly cannot.
I am extremely disappointed that Ivar escaped. I'd hoped for some new conflict in the final season.
When you lose your powerbase, how do you build up from it? Most of the people in Norway, Sweden and Denmark would have heard about Ivar the snake, and they would recognise him through his limping. He would have to stay in the shadows, out from sight of anyone who would recognise. It is not an ideal position for recruiting, but it is ideal if you can make yourself to be a criminal mastermind.
In that way you might get enough of men, especially skilled in assassinations, but it would be very hard to push yourself up and back to be a god at Kattagat. Why would those people elect him to be their leader again?