Explain why it is difficult for a community or a nation to be completely independent

Well most communities use outside sources that they might need.  to be 100% self sustainable you must have certain things.  if you do not have good soil you cannot grow food.  to get good soil you must get it from an outside source which would mean you are relying on someone else and you are not independent.  So you must have necessary things to be independent without trade from other places. 

Doesn't your school check for plagarism?