Yeah the famous '51% attacks'.
I read some of the online resources in the subject, including the one swinglock mentions[1]. And yeah the answers are a bit outdated, like the 2013 on: 'As for the merge, this is still being discussed and we do not have a good contingency plan'. The answer seems to be the 'longest chain wins' ... so that's not a 100% convincing answer.
Is there a way to know the distribution of nodes per country?