This is something that always puzzles me. How come it's accepted as a given that countries cannot seal their borders.
The Soviet Bloc were pretty good at it
EDIT also the border between north and south korea is pretty tight
EDIT also the border between north and south korea is pretty tight
A few thousand unorganised migrant workers who are trying to smuggle themselves in with no more than a suitcase each and try to hide in the corners of soceity when they get there is quite different from a massive uniformed army with tanks and trucks who then try to take over the running of the government when they get here.
Also the army was legally allowed and ordered to shoot the Germans who were trying to come over, whereas they is not the political will to shoot migrant workers.