Isn't it unfair that North Koreans can't know about God? Do they just go to hell? It's not really their fault at all. The leader tells them everything. They have no way of knowing about God, no outside communication whatsoever. Will they go to hell for something they have no control of? Obviously, only God knows, but do you have any thoughts on it?
There have been endless attempts at blocking the spread of Christianity. None worked because Christianity is spread by one Christian teaching others. There is no central point to stop the spread. Worse from an anti-Christian government's point of view, it is Christians who make the best citizens, so how do you stop something that produces people you like? Thus you can read about the frustrations of the Roman Emperors in wiping out Christians -- a story that is repeated through the centuries in different countries.
North Korea has tried to make Christianity illegal, but it hasn't stopped its existence in its borders. For example, North Korean Christians documents the persecution of Christians within North Korea. But think a moment. If Christianity is supposed to be unknown in North Korea, then where are they finding Christians?
One means open to Christians is to teach secular subjects in a restricted country, which gives the opportunity to teach Christianity quietly on the side. See: Teaching the Dragon. Of course, today the Internet makes spreading truth possible in even far away places.
I'm confident that for those wanting to find God, God makes sure they have a way to meet Christians, seemingly just by coincidence. What I suspect is that you are trying to find an exception to the verse that says "in flaming fire taking vengeance on those who do not know God, and on those who do not obey the gospel of our Lord Jesus Christ" (II Thessalonians 1:8). Christians understand that people are already lost on their own. We all sin and without help to get out of sin, we will die in our sins. That is why Christians feel driven to teach everyone the Gospel so that all have an opportunity to be saved.