Let me start with some background, in fiction authors like to explore situations where the human race meets another civilization. As a rule of thumb both races in one way or another - sometimes after a short period of losing - end up having the same level of technology to be capable of fighting each other. As I was building an argument for how fallacious this plot construction is it occurred to me that even better than logical arguments it would be to consider history, however the only occurrence of such a thing I was able to think of of the top of my mind was the Europeans arriving in america. So I was looking for other documented situations where two more or less isolated cultures had developed with differing levels of (military) technology before meeting.
(I am more than willing to do all the research myself, but getting a starting point has proven hard. For example, I suppose that when the romans where expanding this must have happened as well at some point, but from what I was able to find the requirement of some level of isolation did not seem to occur... or was not documented... And as a last note, I know that any war tends to be won by some level of difference in either technology (including logic) or manpower, but what I am looking for is a vast difference)