They do not have formal millitary training but armies will have a hard time attacking a guerilla-tactic defense.
you know that guerillas usually need training superior to that of your average soldier because of how complex guerilla warfare is right?
sure, there are plenty of examples of civilians taking up arms and commencing guerilla warfare...
when they happen to be extremely clever, past that of the average soldier, and happen to be fighting their government or an already occupying force.
this isn't even mentioning the fact that guerilla warfare is completely focused around offensive tactics, right? you can't defend as the guerilla. you can pepper your enemy while they get ready to assault, but that's all you can do. the reason this normally works is because the larger force doesn't know where the guerilla is running off to, for example.
in this case, he might not know your exact base but he's planning to grab the entire area. it's inevitable that he'll find your hideout eventually. this is why guerilla warfare does not work on the defense: guerillas have no good defense.
you cannot defend a country with guerilla warfare. you can only defend an ideology.
the reason why, say, the vietcongs were able to use guerilla warfare is because south vietnam and north vietnam were at something of a stalemate while their stronger allies weren't the ones trying to completely defeat the other half, and in the examples where the forces of the actual nations were not on standby and were actually taking a vietcong fortification, for example, the vietcongs were forgeted.