idk how i feel about them killing the natives......like tbh this isn't their land

You're right, it's not! But tbf, the manga isn't shedding good light on killing the natives anyway. Einar isn't protrayed as some glorious hero for winning their duel. It's actually the opposite imo

true

To be fair, Thorfinn laid down some strict rules and they have a language barrier between them and the natives. There was too much either side didn't understand (I am excluding the disease portion because it was unintentional and uncontrollable at that time.)

It started to fall apart because of those who didn't follow his rules by bringing swords with them (which they received some comeuppance for almost immediately) and by natives of the same mindset, aka a fight for superiority. Thorifinn wanted a partnership and if he had had a year or so to work it out, things could have been better for both parties. He could have had better enforcement and native involvement.

Certainly better than what would happen to the natives when the British showed up.

that's the point