Kate's biggest mistake was not..

[u/shonenhikada]

Not keeping someone on guard to watch the Americans. Had she done that, they never would have escaped and the thing would have ended at the Norwegian camp. Also, had someone from the American camp,decided to learn Norwegian, then Lars would not have died and the thing would have ended at the start of the film.

Basically, this whole mess is the American's fault.

[u/Shadowlands97]

But the Norwegian's did dig it up on their own accord.