There is no such thing as reliable sources that long back
Indeed, but it's not about reliable sources, we are not talking about what truly happened in history, we are talking about the source for the manga. Since they are not reliable, the author might still deviate from it, as a manga is still a work of fiction, but
It's better to be careful, he might follow the sources closely.
Do you have an issue with me spoiling world war 2, the cuban missile crisis too?
No, but you can't compare WW2 and the Cold War to the story that is told there. As I said, what is written in the Vinland Sagas (the main sources for the manga)
is not common knowledge.
Therefore,
Do you have an issue with me spoiling the founding of the Iroquois Confederacy too?
If a work of fiction were to be written on this subject, I would be deeply annoyed if you were to spoil me its end because you knew it from your historical knowledge. Because I had never heard about it before today
but treating history as if it was fiction is absurd, and talking about spoilers in the same sentence as history makes my head spin.
We are not talking about spoiling history, we are talking about spoiling a work of fiction. I call it history spoiler for the sole reason that it is technically not a manga spoiler. Instead of using your manga knowledge to spoil, you use your historical knowledge. If you were to tell someone how VS will end, you would not be spoiling history, you would be spoiling VS. It's not complicated.
Aren't the first three episodes premiering this weekend? When will the other two go up on Amazon—tomorrow?
The first episode was supposed to premiere worldwide more than 5 hours ago, but Amazon Prime is late. The next two's announced release date is tomorrow, July 7th, 3:40PM UTC and 4:10PM UTC.